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Reduced Portion
For 2020-21 Public Exam Only
S.JAYACHANDRAN
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1.2.13. Define ‘Electric field’.
Force experienced by a unit charge at a point
1.2.1. What is meant by quantisation of charges?
is
known
as electric field unit: NC-1
The charge q is equal to an integral multiple
1.2.14 Define ‘electrostatic potential”.
of fundamental charge e. q = ne
Work done by an external force to bring a
1.2.2. What are the differences between Coulomb force
unit positive charge with constant velocity from
and gravitational force?
infinity to the point, is electrostatic potential at that
point. unit: volt
1.2.15 Write down Coulomb’s law in vector form and
mention what each term represents.
1)The force exerted on charge 𝑞1 by charge 𝑞2 is
1. Electrostatics
1.2.3. What is corona discharge
Reduction of total charge of the conductor
near the sharp edge is called action at points or corona
discharge.
1.2.4.State Gauss Law
The total electric flux 𝛟 E through a
closed surface is equal to 1/𝜀 0 times
net charge in the surface.
1.2.5. Write down the Applications of capacitors
1. Used in flash camera for releasing energy.
2. Used in heart defibrillator
3. Used in the ignition system of automobile engines
to eliminate sparking
4. Used to reduce power fluctuations in power
supplies
1.2.6. Define ‘Electric dipole’
Two equal and opposite charges separated by a small
distance constitute an electric dipole.
Examples:
CO,
water,
ammonia,
HCl
1.2.7. Define electric flux.
Total number of electric field lines crossing a area
Normally, is known as electric flux.
unit : N m2 C-1
1.2.8. What is the general definition of electric dipole
moment?
Dipole moment is equal to product of magnitude of
charge and distance. p=q.2a. Unit :C m
1.2.9. Define ‘electrostatic potential energy?.
Work done to assemble the system of charges
in a configuration is Electrostatic potential energy.
1.2.10. What is meant by electrostatic energy density?
Electric Energy stored per unit volume is called
electrostatic energy density.
1.2.11.Define ‘capacitance’. Give its unit.
Ratio of the magnitude of charge on any one
of the conductor plates to the potential difference
between the conductors, is the capacitance C of a
capacitor. unit: Farad
1.2.12. What is meant by superposition principle.
Total force on a charge is equal to vector sum
of all forces acting on the charge.
𝑟̂
21 is a unit vector from charge 𝑞2 to charge 𝑞1
2)The force exerted on charge 𝑞2 by charge 𝑞1 is
𝑟̂
12 is a unit vector from charge 𝑞1 to charge 𝑞2
1.3.1 Derive an expression for electrostatic potential due
to a point charge.
Work done to move a positive charge from
infinity to a point with constant velocity is the
electric potential at that point.
P is a point at a distance r from the charge q.
1.3.2 Explain in detail Coulomb’s law and its aspects.
1.Electrostatic force is directly proportional to the
product of two charges and is inversely
proportional to the square of the distance between
the two charges.
2.Electrostatic force is along the line joining the two
charges.
3.Coulomb’s law is similar as Newton’s law of
gravitation.
4.Electrostatic force is always greater than
gravitational force
5.Electrostatic force depends on nature of the
medium.
6.Coulomb force is true only for point charges.
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1.3.3 Derive an expression for Torque experienced by
an electric dipole in the uniform electric field
An electric dipole of dipole moment p is placed
in a uniform electric field. Two forces qE and _-qE act
on +q and -q. The total force acting on the dipole is
zero. These two forces acting at different points will
constitute a couple and the dipole experience a
torque.
This torque rotates the
dipole and aligns it with
the electric field
If initial position Ɵ’ = 900
Potential energy stored in dipole
kept in the uniform electric field
1.3.6 Obtain the expression for capacitance for a
parallel plate capacitor.
Consider a capacitor with two parallel plates
1.3.4 Obtain an expression for potential energy due to a
collection of Two charge and three-point charges which each of cross-sectional area A and separated by a
distance
are separated by finite distances.
1.3.7 Derive the expression for resultant capacitance,
when capacitors are connected in series .
Three capacitors of capacitance C1, C2 and C3
connected in series with a battery of voltage V.
Each capacitor stores the same charge Q. Voltage
across each capacitor V1, V2 and V3 are different.
1.3.5 Derive an expression for electrostatic potential
energy of the dipole in a uniform electric field
An electric dipole of dipole moment p is
placed in the uniform electric field E. The dipole
experiences a torque which rotates the dipole to align
along the electric field.
To rotate the dipole against the torque, an equal
and opposite external torque must be applied on the
dipole.
The work done by external torque to rotate the
dipole from angle Ɵ′ to Ɵ at constant angular velocity is
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1.3.8 Derive the expression for resultant capacitance,
when capacitors are connected in parallel.
Three capacitors of capacitance C1, C2 and C3
connected in parallel with a battery of voltage V
Voltage across each capacitor is Same as V.
Each capacitor stores different charges Q 1, Q2, Q3
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1.5.1Calculate the electric field due to a dipole on its
axial line
An electric dipole is placed along the X-axis. C is a
point at a distance r from O on the axial line.
1.3.9 Obtain the expression for energy density of a
Parallel plate capacitor
Capacitor stores charge and energy. To store
the charge, work is done by the battery. This work
done is stored as electrostatic potential energy 𝑼𝑬 in
the capacitor.
1.5.2 Calculate the electric field due to a dipole on its
equatorial plane
An electric dipole is placed along the X-axis.
C is a point at a distance r from O on the equatorial
plane.
1.3.10 Explain in detail the effect of a dielectric placed
in a parallel plate capacitor
The direction of ⃗⃗⃗⃗
𝐸+ is along BC and the
direction of ⃗⃗⃗⃗
𝐸− is along CA. On resolving
Vertical components𝐸+ Sinθ and 𝐸− Sinθ are
equal and opposite. So, they cancel each other.
Horizontal Components 𝐸+ Cosθ and𝐸− Cosθ
add together to give resultant Electric field.
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Direction of Electric field is opposite to dipole
moment.
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1.5.4 Explain in detail the construction and working of
a Van de Graaff generator.
Device produces potential difference of 107 V.
Principle: Electrostatic induction and action at
points.
Construction:
1. A hollow spherical conductor is fixed on the
insulating stand.
2. A pulley B is placed at the center of the hollow
sphere and another pulley C is fixed at the bottom.
3. A belt made up of silk or rubber runs over both
pulleys.
4. The pulley C is run by the electric motor.
5. Two metallic combs E and D are fixed near the
pulleys.
6. The comb D is given potential of 104 V.
7. The upper comb E is connected to the inner sphere.
Direction of Electric field is opposite to dipole moment.
1.5.3 Derive an expression for electrostatic potential
due to an electric dipole.
An electric dipole is placed along the X-axis.
P is a point at a distance r from O.
Working
1. High electric field near comb D, ionizes the air.
2. Due to action of points, belt gets positive charges
and negative charges are attracted towards the
comb D.
3. When the positive charges reach the comb E, Due
to electrostatic induction , Comb E gets negative
charge and sphere gets positive charge.
4. The positive charges are distributed uniformly on
the outer surface of the hollow sphere.
5. Due to corona discharge , positive charges in the
belt are cancelled and down going belt does not
carry charge.
6. At the bottom, it again gains a large positive charge.
7. This process continues till sphere produces the
potential difference of 107 V.
8. The leakage of charges can be reduced by enclosing
the machine in a gas filled steel chamber at very
high pressure.
Uses
The high voltage produced is used to accelerate
positive ions (protons and deuterons) for nuclear
disintegrations.
1.5.5 Obtain the expression for electric field due to an
infinitely
long
charged
wire.
Consider an infinite long straight wire having
linear charge density λ(charge present per unit
length). Let P be a point at a distance r from the wire.
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The resultant electric field will be same at all
points equidistant from the wire and directed
radially outwards.
A cylindrical Gaussian surface of radius r and
length L is taken.
1.5.7 Obtain the expression for electric field due to an
charged spherical shell.
Consider a uniformly charged spherical shell
of radius R carrying total charge Q. Let P be a point
at a distance of r from the centre of sphere.
If wire is negative charged, E acts inwards and if wire
is positive charged, E acts outwards.
1.5.6 Obtain the expression for electric field due to an
infinitely long charged sheet
Consider an infinite plane sheet of charges Case 1. At a point outside the shell (r > R)
with uniform surface charge density σ (charge a spherical Gaussian surface of radius r is taken.
present per unit area). Let P be a point at a distance
of r from the sheet.
Resultant electric field is same at all points
equidistant from the plane and radially directed outward
at all points.
A cylindrical Gaussian surface of length 2r and
two flats surfaces each of area A is taken.
Case 2. At a point on the surface of the spherical shell
(r = R)
The electrical field at points
on the spherical shell
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Case 3. At a point inside the spherical shell (r < R) 2.2.7.State Kirchhoff’s voltage rule.
Since Gaussian surface encloses no charge, Q = 0.
In a closed circuit the algebraic sum of the
No charge is present inside the sphere. electric field is products of the current and resistance is equal to the
zero at all points inside the shell.
algebraic sum of emf in the circuit.
2.2.8. What is electric power and electric energy?
1.3.11 Deduce Gauss law from coulombs law
Electrical power P is the rate at which the
electrical potential energy is used. Unit: watt
Electric energy is the product of electric Power
and Time. Unit: Watt hour
2.2.9. Define current density.
Current per unit area of cross section of the
conductor iscalled current density (J). Unit: A m 2
2.2.10. State ohm’s Law
Resistance of a conductor is equal
to ratio of Voltage applied to current
flowing in the conductor.
2.2.11. Why touching a electrical connection with the
wet skin is always dangerous.
Resistance of dry skin is high around 500 k Ω.
But when the skin is wet, the resistance decreases to
around 1000 Ω. While touching electric components
2.CURRENT ELECTRICITY
with wet hand, due to low resistance, large current
2.2.1Why current is a scalar?
flows in our body which is dangerous
Current has both magnitude and direction .But
2.2.12.Is battery a source of electrons?
the direction of current does not obey vector laws of
No, Battery is a source of electrical energy,
addition .So, Current is a scalar quantity.
due to which these electrons in the conducting wire
2.2.2 Distinguish between drift velocity and mobility.
flow in a particular direction.
Drift velocity
Mobility
2.2.13.What is meant by internal resistance of a cell?
Average velocity
Magnitude of the drift
Resistance given by electrodes and electrolyte
acquired by the electrons velocity per unit
of a battery against the flow of charges within the
in an Electric field.
Electric field.
battery, is called internal resistance r of a cell.
Vectot Quantity
Scalar Quantity
2.2.14. What is Seebeck effect?
-1
2 -1 -1
In a closed circuit made of two dissimilar
Unit: ms
mV s
metals, when the junctions are maintained at
2.2.3. What are ohmic and non ohmic devices?
different temperatures an emf is developed.
Ohmic Devices
Non Ohmic Devices
2.2.15. State the applications of Seebeck effect.
Materials or devices that
Materials or devices that 1.Seebeck effect is used in thermoelectric generators,
obey Ohm’s law
do not obey Ohm’s law
to convert waste heat into electricity.
2.Used in automobiles for increasing fuel efficiency.
A Graph of I against V is A Graph of I against V
3.Used in thermocouples to measure the temperature
linear(Straight Line)
is non-linear
difference.
2.2.4. Define electrical resistivity.
2.2.16. What is Thomson effect?
Resistance of a conductor of unit length and
If two points in a conductor are at different
unit area of cross section is known as electrical
temperatures, electron density changes at them. So,
resistivity ρ of a material .
potential difference is created between these points.
Unit: ohm-metre (Ω m).
2.2.17Derive the expression for power P=VI in
electrical circuit and write its various forms
2.2.5. Define temperature coefficient of resistance.
Ratio of increase in resistivity per degree rise
in temperature to its resistivity at T .
Unit : per 0C.
2.2.18. What is Peltier effect?
2.2.6. State Kirchhoff’s current rule.
When current is passed through a
Algebraic sum of the currents at any junction thermocouple, heat is evolved at one junction and
of a circuit is zero.
absorbed at the other junction.
o
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2.3.1. Obtain the condition for bridge balance in 2.3.4.Explain the determination of unknown resistance
Wheatstone’s bridge.
using meter bridge.
Meter bridge consists of one meter manganin
wire AB connected between copper strips Cand D.
Unknown resistance P is connected in gap G 1 and a
Known resistance Q is connected in gap G 2. A jockey
is connected to the central terminal E through a
galvanometer (G) and a high resistance (HR). A
Lechlanche cell and a key (K) are connected across the
ends of the bridge wire.
The jockey is adjusted on the wire so that the
galvanometer shows zero deflection. Let the point be
J. The lengths AJ=l1 and JB=l2 of the bridge wire now
replace the resistance R and S of the Wheatstone’s
2.3.2 Explain the determination of the internal bridge. r is the resistance per unit length of wire
resistance of a cell using voltmeter.
The emf of cell ε is measured by connecting a
high resistance voltmeter across it in a open circuit.
The voltmeter reading gives the emf of the cell.
External resistance R is included in the circuit
and current I flows in the circuit. The potential
difference across R is equal to the potential
difference across the cell (V).
2.5.1 Explain the determination of the internal
resistance of a cell using potentiometer.
Connections are given as in the circuit to
determine the internal resistance of a cell.
With K2 open, no current
flows in resistor R, so it
becomes open circuit.
Let CJ = l1 is the balancing
length for the emf,
2.3.3 Obtain the macroscopic form of Ohm’s law from
its microscopic form and discuss its limitation.
l is the length and A is cross sectional area of When key K2 is closed, current flows in resistor R, so
it becomes closed circuit
a wire. V is the potential difference applied across
the wire. E is the net electric field in the wire.
By microscopic form of ohm’s law
This is the macroscopic form of ohm’s law. This law
cannot be applied for Non-Ohmic Materials.
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2.5.2 Describe the microscopic model of current and
obtain general form of Ohm’s law
A is the area of cross section of a conductor, E is
the applied electric field. n is the number of free
electrons per unit volume. vd is the drift velocity of
the free electrons.
Equivalent resistance is the sum of the individual
resistances
2)Three Resistors of resistance R1, R2 and R3
connected in Parallel with a battery of voltage V.
Voltage across each Resistor is Same.Different
Current I1,I2 and I3.are flowing through each resistors.
current density ( J ) is defined as the current per unit
area of cross section of the conductor .
3.Magnetism and Magnetic effects of
electric current
𝜎 is conductivity of the material of the conductor
This equation is called microscopic form of ohm’s law.
2.5.4. Explain the equivalent resistance of a series and
parallel resistor network.
Three Resistors of resistance R1, R2 and R3
connected in series with a battery of voltage V.
Same Current passes through each Resistor.
Voltage across each resistor V1, V2 and V3 are
different.
3.2.1. State Coulomb’s inverse law in magnetism.
Force of attraction or repulsion between two
magnetic poles is directly proportional to the
product of their pole strengths and inversely
proportional to the square of the distance between
them.
3.2.2. State Ampere’s circuital law.
Line integral of magnetic field over a closed
loop is equal to μ0 times net current enclosed by the
loop.
3.2.3. Define magnetic dipole moment.
Product of pole strength and magnetic length of
a magnet is called magnetic dipole moment 𝒑𝒎.
direction of 𝒑𝒎 acts from south to north pole.
Unit: 𝐀 𝐦𝟐
3.2.4.State Right hand thumb rule
Current carrying conductor is held in right hand
such that the thumb points in the direction of current
, then the fingers encircling the wire gives the
direction of the magnetic field lines produced
3.2.5.State Right hand palm rule
The current carrying solenoid is held in right
hand such that fingers curl in the direction of
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current, then extended thumb gives the direction of 3.3.2.Write the Properties of magnet
magnetic field
1) A Suspended bar magnet will always point
3.2.6. Define magnetic flux.
along the north-south direction.
Number of magnetic field lines crossing per unit
2) The attractive force of a magnet is maximum
area normally is called magnetic flux. Unit: weber
near the end of the bar magnet.
3) When a magnet is broken into pieces, each
3.2.7. State Biot-Savart’s law.
piece is a magnet.
Magnitude of magnetic field varies
4) Poles of a magnet have equal pole strength.
(i) directly as the current I
5) The ratio of magnetic length and geometrical
(ii) directly as the length of current element
length is 5/6.
(iii) directly as sine of the angle between Idl and r.
3.3.3 Give an account of magnetic Lorentz force.
When an electric charge q is moving with
(iv) inversely as the square of the distance r.
⃗ , it experiences a
3.2.8.How a galvanometer is converted into an velocity 𝐯⃗ in the magnetic field 𝐁
ammeter.
force, called magnetic Lorentz force ⃗⃗⃗⃗⃗
𝑭𝒎 .
By connecting a low resistance in parallel with
the galvanometer
3.2.9.How a galvanometer is converted into a voltmeter. 1) Force is directly proportional to the magnetic
By connecting high resistance Rh in series
⃗.
field 𝐁
with galvanometer.
2) Force is directly proportional to the velocity 𝐯⃗ of
3.2.10.Define Current sensitivity of a galvanometer
the moving charge
Deflection produced per unit current flowing 3) Force is directly proportional to sine of the angle
through a Galvanometer.
between the velocity and magnetic field
3.2.11 What is resonance condition in cyclotron?
4) Force is directly proportional to the charge q
frequency f at which the positive ion 5) The direction of Force 𝐅
⃗⃗⃗⃗⃗𝐦 is always
circulates in the magnetic field must be equal to the
⃗⃗
perpendicular to 𝐯⃗ and 𝐁
constant frequency of the electrical oscillator fosc. 6) The direction of Force on negative charge is
This is called resonance condition
opposite to the direction of force on positive
3.2.12.How to increase Current sensitivity of a
charge
Galvanometer
7) If the charge q is moving along magnetic field
1) by increasing the number of turns N
then, force is zero
2) by increasing the magnetic induction B
3.3.4 How is a galvanometer converted into an
3) by increasing the area of the coil A
ammeter?
4) by decreasing the couple per unit twist of the
A galvanometer is converted into an ammeter
suspension wire .
by connecting a low resistance in parallel with the
3.2.13.Why Phosphor - bronze wire is used as the
galvanometer. This low resistance connected in
suspension wire in a galvanometer
parallel is called shunt resistance S
Phosphor - bronze wire has very small couple per unit
Let I be the current passing through the
twist.
ammeter. Let Ig be the current passing through the
3.2.14 Is an ammeter connected in series or parallel in a galvanometer of resistance Rg and the remaining current
circuit? Why?
(I – Ig) through shunt resistance S.
An ammeter is a low resistance instrument
which is always connected in series to the circuit.
ammeter will not change current largely in the
circuit. If ammeter is connected in parallel, due to low
resistance large current will flow in it thereby
decreasing current in the main circuit
3.3.1. Write the Properties of Magnetic field lines
1) Magnetic field lines are continuous closed curves.
2) The tangent to the magnetic field lines gives the
direction of magnetic field at any point.
1) An ammeter is a low resistance instrument and it
3) Magnetic field lines never intersect each other.
is always connected in series to the circuit
4) When the magnetic field is strong, magnetic field 2) An ideal ammeter has zero resistance
lines are crowded and when the magnetic field is 3) To increase the range of an ammeter n times,
weak, magnetic field lines are apart.
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3.3.5 How galvanometer is converted into voltmeter?
A galvanometer is converted into a voltmeter
by connecting high resistance Rh in series with
galvanometer.
Let Rg be the resistance of galvanometer and Ig be the
current with which the galvanometer produces full scale
deflection. Current in the electrical circuit is same as
the current passing through the galvanometer.
3.5.2 Obtain a relation for the magnetic field at a point
along the axis of a circular coil carrying current.
R is the radius of a current carrying circular
1) Voltmeter is a high resistance instrument and it
is always connected in parallel with the circuit
loop and I is the current flowing through the wire .
2) An ideal voltmeter has infinite resistance
P is a point on the axis of the circular coil at a
3) In order to increase the range of voltmeter n times,
distance z from the centre of the coil O. Two
diametrically opposite current line elements of the coil
3.5.1Find the magnetic induction due to a long straight
each of length ⃗⃗⃗
𝑑𝑙 are taken at C and D.
conductor using Biot- savart law
Let YY’ be an infinitely long
straight conductor and I be the steady current
through the conductor . P is a Point and at a distance
a from the wire. A small length AB=dl is considered
as current element I.dl at a distance r from point P.
perpendicular AC is drawn to the line BP. Let ф be the
Magnetic field at P due to current element at C
angle between AP and OP and dф be the angle between
is along PR and due to current element D is along PS.
AP and BP.
Horizontal components dBcosϕ cancel out. while the
vertical components dBsinϕ alone contribute to the
⃗⃗ at the point P.
net magnetic field 𝑩
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3.5. 3 Derive the expression for the force on a currentcarrying conductor in a magnetic field
dl is the length of small element of conductor placed
in magnetic field B, with cross-sectional area A.
3.5.5 Derive the expression for the force between two
parallel, current-carrying conductors.
The free electrons drift opposite to the direction of
current I. relation between current I and drift velocity
𝐯⃗⃗⃗⃗𝒅 is
A and B are two long
straight parallel conductors
separated by a distance r
kept in air medium.
I1 and I2 are the currents
passing through
A and B in same direction
(along z - direction).
By thumb rule
3.5.4 Derive an expression for Magnetic field due to a
long current carrying solenoid
Consider a solenoid of length L having N turns.
Applying Ampère’s circuital law for the rectangular
loop abcd
3.5.6 Explain the principle and working of Moving coil
galvanometer
Moving coil galvanometer is a device used to detect
the flow of current in an electrical circuit.
Principle: When a current carrying loop is placed in
a uniform magnetic field, it experiences a torque
Construction: Rectangular coil PQRS made of
insulated thin copper wire is wound over a light
metallic frame. The coil is suspended freely in a radial
magnetic field produced by horse-shoe magnet.
The upper end of coil is attached to phosphor
bronze strip and the lower end of the coil is connected
to phosphor bronze hair spring. By using small plane
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mirror, lamp and scale, deflection of the coil is
measured. Suspension strip and the spring S are
connected to voltage terminals.
Working
In the radial magnetic field, parallel sides QR and SP
experience no force. Perpendicular sides PQ and RS
experience equal forces in opposite directions. Due to
this, torque is produced
G is called galvanometer constant or current reduction
factor of the galvanometer.
3.3.6 Explain the concept of velocity selector
By using proper electric and magnetic fields, charges
moving with particular speed can be selected in an
arrangement called velocity selector.
Electric field 𝐸⃗ acts between two parallel plates.
uniform magnetic field ⃗⃗⃗𝐵 acts perpendicular to the
direction of electric field 𝐸⃗.Net force on charge q
entering with velocity v is
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3.3.7 Discuss the motion of charged particle in magnetic
field.
Consider a charged particle of charge q
⃗⃗
having mass m entering uniform magnetic field 𝑩
with velocity 𝐯⃗. velocity v
⃗ is perpendicular to the
⃗ . Lorentz force 𝐹 acts on the charge
magnetic field 𝐵
⃗ and velocity v
perpendicular to both magnetic field 𝐵
⃗.
charged particle moves in a circular orbit of radius r.
⃗ = 𝒒 (𝐯⃗ 𝑿 𝑩
⃗⃗ )
𝑭
If a charged particle moves in magnetic field
such that its velocity is not perpendicular to the
magnetic field, the path of the particle is not a circle
it is helix around B.
3.3.8 Find the magnetic field due to a long straight
conductor using Ampere’s circuital law.
I is the current flowing in a straight
conductor of infinite length. An amperian loop in the
form of a circular shape is taken at a distance r from
the centre of the conductor.
By Ampere’s circuital law
Charges having this velocity v are selected to come out.
3.2.15 Why is the path of a charged particle not a circle
when its velocity is not perpendicular to the magnetic
field?
Resolving particle velocity with respect to
magnetic field, the parallel component of velocity
vCosѲ remains unchanged and drags the charge
along magnetic field. The perpendicular component
of velocity vSinѲ keeps changing in direction due to
Lorentz force and makes the charge to rotate. Hence
the path of the particle is not a circle; it is a helical
around the magnetic field.
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closed circuit changes, an emf is induced in the
circuit.
4.2.12 State Faraday’s laws of electromagnetic
4.2.1 State Lenz’s law.
Direction of the induced current will oppose induction.
First law : Whenever magnetic flux linked with a
the cause that produces it.
closed circuit changes, an emf is induced in the
circuit.
4.2.2 State Fleming’s righthand rule.
The thumb, index finger and middle finger of right hand Second law: The magnitude of induced emf is equal
to the rate of change of magnetic flux.
are in mutually perpendicular directions.
4 ELECTROMAGNETIC INDUCTION
AND ALTERNATING CURRENT
If the index finger points the direction of the
magnetic field and the thumb points the direction of
motion of the conductor, then the middle finger will
point the direction of the induced current.
4.2.3 Mention the ways of producing induced emf.
1) By changing the magnetic field B
2) By changing the area A of the coil and
3) By changing the orientation θ of the coil with
magnetic field.
4.2.4How will you define RMS value of an alternating
current?
The root mean square value of an alternating
current is defined as the square root of the mean of
the squares of all currents over one cycle.
4.2.5How will you define Q-factor?
Ratio of voltage across L or C to the applied voltage
is called Quality or Q-factor
4.2.6 What is meant by wattles current?
If the power consumed by current in an AC
circuit is zero then that current is called wattles current
4.2.7 What do you mean by resonant frequency?
The frequency at which resonance takes place
so that impedance is minimum and current is
maximum is called resonant frequency.
4.2.8 What are the Advantages of AC over DC
1) AC can be produced cheaper than DC.
2) AC transmission loss is small compared to DC
transmission.
3) AC can easily be converted into DC with the help
of rectifier
4.2.9 What are the disadvantages of AC over DC
1) Alternating voltages cannot be used for charging
of batteries, electroplating, electric traction etc.
2) At high voltages, AC is more dangerous to work
than DC.
4.2.10 What are phasors?
A rotating vector which rotates about the
origin in anti-clockwise direction at a constant
angular velocity ω to represent a sinusoidal
alternating voltage is called Phasor.
4.2.11 What is meant by electromagnetic induction?
Whenever the magnetic flux linked with a
4.2.13What for an inductor is used with some examples
Inductor is a device used to store energy in a
magnetic field when an electric current flows
through it. Example: Coils, Solenoids and Toroids.
4.2.14What do you mean by self-induction?
When current flowing in a coil is changed ,an
emf is induced in that same coil.
4.2.15What is meant by mutual induction?
When current flowing in a coil is changed ,an
emf is induced in other near coil.
4.2.16 What are step-up and step-down transformers?
Step-up transformer converts low alternating
voltage into high alternating voltage.
Step-down
transformer
converts
high
alternating voltage into low alternating voltage.
4.2.17 Define average value of an alternating current.
Average of the positive current values
or
negative current values is called average value of an
alternating current.
4.2.18Define electric resonance.
When the frequency of the applied alternating
source is equal to the natural frequency of the RLC
circuit, the current is maximum. The circuit is in
electrical resonance and frequency is resonant
frequency.
4.2.19 Give any one definition of power factor.
Power factor = cos ϕ = cosine of the angle of lead or
lag between current and resultant voltage.
4.2.20What are LC oscillations?
Oscillations of energy in a pure LC circuit,
between the magnetic energy of the inductor and the
electrical energy of the capacitor of definite
frequency are called are called LC oscillations.
4.2.21Define Self Inductance
Self-inductance of a coil is defined as the flux
linkage with coil when one Ampere current flows in
the coil. Unit: henry
4.2.22Define Mutual Inductance
Mutual inductance M21 is defined as the flux
linkage with coil 2 when one Ampere current flows
in coil 1. Unit: henry.
4.2.23How will you define the unit of inductance?
Henry is the inductance of a coil when one
Ampere current flowing in coil produces unit flux
linkage in the same coil.
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4.2.24 What do you understand by self-inductance of a
coil? Give its physical significance.
Self-Inductance of a coil opposes the change
in current flowing in it and tries to maintain the
original current. Inductance in a circuit plays the role
of inertia and moment of inertia in mechanical motion.
4.3.1 Mention the various energy losses in a
transformer.
Flux leakage: Energy is lost when the magnetic lines
of primary coil are not completely linked with
secondary coil. This flux leakage is minimized by
winding coils one over the other.
Copper loss : Energy is lost due to Joule heating,
when an electric current flows through Transformer
windings, This copper loss is minimized by using thick
wires.
Core loss or Iron loss:
1)Energy is lost in the form of heat, when
transformer core is magnetized and demagnetized
repeatedly by the alternating voltage. Hysteresis loss is
minimized by making transformer core using silicon
steel.
2)Energy is lost in the form of heat, when eddy
currents are induced due to Alternating magnetic
flux in the core. Eddy current loss is minimized by
using laminated transformer core.
4.3.2. How much energy is stored in an inductor of
inductance L while establishing the current in it?
Whenever current is changing in the inductor
circuit, the inductance opposes the change in current.
work is done by some external agency to change the
current. This work done is stored as magnetic potential
energy.
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Inductance depends on the geometry of the solenoid and
the medium present inside the solenoid.
4.3.4.Derive an equation for Mutual inductance between
two long co-axial solenoids
l is the length, A1,A2 is the cross-sectional
area and n1,n2 is the number of turns per unit length
of the two long solenoids 1 and 2. When i1 current
passes through the solenoid 1,a magnetic field 𝑩𝟏 is
produced in it.
4.3.5.Obtain an expression for motional emf from
Lorentz force.
A conductor rod AB of length l moves right
with a velocity v in a magnetic field B acting
perpendicular inwards. Free electrons inside the rod
experiences downward Lorentz force and gets collected
at end A of the rod.
Collection of free electrons at end A produces
4.3.3.Derive an equation for Self inductance of a solenoid Electric field E. electric field exerts upward coulomb
l is the length, A is the cross-sectional area force and stops further collection of free electrons at
and n is the number of turns per unit length of the end A. So, Potential difference is induced across the
solenoid. When current i passes through the ends of the rod.
solenoid, magnetic field is produced in the solenoid.
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applied voltage and the current
are in phase in a resistive circuit
4.3.8 Derive an expression for RMS value of AC
The root mean square value of an alternating
This emf produced due
current
is defined as the square root of the mean of
to the movement of the rod, is known as motional emf.
the squares of all currents over one cycle. Alternating
current is given by 𝒊 = 𝒊𝒎 𝑺𝒊𝒏𝝎𝒕
4.3.6.How will you induce an emf by changing the area
enclosed by the coil?
Metal rod of length l moves left with a velocity
v on a rectangular metal frame. Metal frame is placed
in a normal magnetic field.
As the rod moves from AB to DC in a time dt, the
area and the magnetic flux through the loop
decreases. So, an emf is induced in the loop.
Due to motional emf, direction of induced current is
clockwise given by Fleming’s right-hand rule.
4.3.7 Find out the phase relationship between voltage
and current in a pure resistive circuit.
A pure resistor of resistance R is connected across an
alternating voltage source.
4.5.1.Explain the construction and working of transformer .
Transformer is a stationary device used to
transform electrical power from one circuit to
another without changing its frequency
Principle : Mutual induction between two coils.
Construction: Two insulated coils are wound over
laminated core of silicon steel. core and coils are kept
in a container filled with suitable medium for better
insulation and cooling purpose.
Working: When alternating voltage is fed to primary
coil P, an alternating magnetic flux is set up in the
laminated core. So, emf is induced in both primary
and secondary coils S. For both primary and
secondary coils, rate of change of magnetic flux per
each turn is same.
By Kirchoff’s loop rule the algebraic sum of potential
differences in a closed circuit is zero
𝜺𝑷 , 𝑽𝑷 , 𝑵𝑷 are the induced emf, applied ac Voltage
and number of turns of the primary coil respectively.
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𝜺𝑺 , 𝑽𝑺 , 𝑵𝑺 are the induced emf, drawn ac Voltage and
number of turns of the Secondary coil respectively.
For Step up transformer K>1, 𝑵𝑺 >𝑵𝑷 , 𝑽𝑺 >𝑽𝑷 , 𝑰𝑺 < 𝑰𝑷
voltage is increased but current is decreased.
Step down transformer K<1, 𝑵𝑺 < 𝑵𝑷 ,𝑽𝑺 < 𝑽𝑷 , 𝑰𝑺 > 𝑰𝑷
voltage is decreased but current is increased.
Ratio of the useful output power to the input power
is known as Efficiency of a transformer.
4.5.2 Derive an expression for phase angle between the
applied voltage and current in a series RLC circuit.
A resistor of resistance R, a inductor of
inductance L and a capacitor of capacitance C are
connected in series across an alternating voltage.
𝐯 = 𝑽𝒎 𝑺𝒊𝒏𝝎𝒕
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𝑽𝑹𝑴𝑺 𝑰𝑹𝑴𝑺 is called apparent power and cos ϕ is
power factor. The average power of an AC circuit is
known as true power of the circuit.
net voltage drop across L-C combination is VL – VC 4.5.4 Find out the phase relationship between voltage
and current in a pure inductive circuit.
which is represented by a phasor OD.
A pure inductor of inductance L is connected
By parallelogram law, the diagonal OE gives the
across an alternating voltage source.
resultant voltage V of VR and (VL – VC)
If XL > X C, (X L−XC) is positive and phase angle ϕ is
positive.
,
If XL < X C, (X L−XC) is negative and phase angle ϕ is
negative.
,
If XL < X C, (X L−XC) is zero phase angle ϕ is zero.
4.5.3 Obtain an expression for average power of AC
over a cycle. Discuss its special cases.
Power is given by the product of the voltage and
current. In an AC circuit, the voltage and current vary
continuously with time. So, power at an instant is
calculated and then it is averaged over a complete cycle.
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The quantity ωL acts as resistance called inductive
reactance (X L) in inductive circuit. unit: ohm.
For Direct current, f = 0. ⸫ XL = 0. Thus an ideal Case(ii)When stored charge is zero in capacitor q=0
inductor offers no resistance to steady DC current.
and current is maximum i=𝑰𝒎 in inductor.
4.5.5Find out the phase relationship between voltage
and current in a pure capacitive circuit.
A capacitor of capacitance C is connected
across an alternating voltage source.
Total energy is fully
magnetic energy
Case(iii)When stored charge is q in capacitor and
current is i in inductor.
By conservation of energy, total energy of the system
remains constant.
4.5.1Show mathematically that the rotation of a coil in
a magnetic field induces an alternating emf.
A Rectangular coil of N turns is rotated with a
angular velocity ω in magnetic field B about an axis
perpendicular to B.
When t =0 plane of coil is perpendicular to B, magnetic
flux is maximum.
When plane of coil is inclined to B at an angle Ѳ,
magnetic flux linkage is
The quantity 1/Cω acts as resistance and is called
capacitive reactance (X C) in capacitive circuit. unit:
ohm. For Direct current, f = 0. ⸫ XC = ∞. So, an
ideal capacitor blocks steady DC current.
4.5.6 Show that the total energy is conserved during
LC oscillations.
In LC oscillations , energy U
oscillates between electric energy 𝑼𝑬 of a capacitor and
magnetic energy 𝑼𝑩 of a inductor.
Induced
Emf
by
faraday law
Magnetic and electric energy vary with time, but the
total energy remains constant .
Case(i) When stored charge is maximum in capacitor As the induced emf varies as sine function of the time
q=𝑸𝒎 and current i is zero in inductor. Total energy angle ωt, it is called sinusoidal emf or alternating emf.
is fully electrical energy
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5 ELECTROMAGNETIC WAVES
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5.2.10How are gamma rays produced ?give its uses
5.2.1.What is displacement current?
Current produced in the region where the electric
field and the electric flux are changing with time is
known as displacement current.
5.2.2.What is meant by Fraunhofer lines?
Dark lines in the solar spectrum are known as
Fraunhofer lines. By comparing absorption spectra 5.3.1Write the properties of electromagnetic waves.
for various materials, Fraunhofer lines helps in 1) Electromagnetic waves are produced by
accelerated charge.
identifying elements present in the Sun’s atmosphere
5.2.4 How are radio waves produced and give its uses 2) Electromagnetic waves do not need any medium
for propagation. So,they are non-mechanical waves
3) Electromagnetic waves are transverse in nature.
4) Electromagnetic waves travel with the speed of
light in vacuum.
5.2.5 How are microwave produced and give its uses
5.2.6 How are infrared waves produced and give its uses
5.2.7 How are visible light produced and give its uses
5.2.8 How is UV light produced and give its uses
5.2.9 How are X-rays produced and give its uses
5) speed of electromagnetic wave v in any medium is
less than speed in vacuum c . v < 𝑐
6) Electromagnetic waves are not deflected by electric
field or magnetic field.
7) Electromagnetic waves can show interference,
diffraction and polarisation.
8) Electromagnetic waves carries energy, momentum
and angular momentum.
5.5.1What is emission spectra? Give their types.
Emission spectra
Spectrum obtained from self luminous source
directly is called emission spectrum. Each source has
its own characteristic emission spectrum.
Emission spectra is classified into 3 types
1.Continuous emission spectra
Contains wavelengths of all visible colours from
violet to red.Spectrum obtained from carbon arc,
incandescent solids are continuous spectra.
2.Line emission spectrum
Contains sharp lines of definite wavelengths. Such
spectra arise when atoms of elements are excited.
Reveals the characters of the element. Different for
different elements. Spectrum of atomic hydrogen,
helium.
3.Band emission spectrum
Contains closely spaced overlapping spectral lines
forming bands and separated by dark spaces. Such
spectra arise when the molecules are excited.spectrum
has a sharp edge at one end and fades out at the other
end. Band spectrum is the characteristic of the molecule
hence, the structure of the molecules can be studied
using their band spectra.
Spectra of ammonia gas in the discharge tube etc.
5.2.3 Why are electromagnetic waves non-mechanical
Electromagnetic waves do not require medium to
travel. But mechanical waves require medium to travel.
So, electromagnetic waves are non-mechanical.
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5.5.2. What is absorption spectra?. Give their types.
Absorption spectra
Spectrum obtained from light, after passing
through a medium or an absorbing substance is
called absorption spectrum. Each substance has its own
characteristic emission spectrum.
Absorption spectra is classified into 3 types
Continuous absorption spectrum
When white light passes through a blue glass
plate, it absorbs all colours except blue. This is an
example of continuous absorption spectrum.
Line absorption spectrum
When white light from carbon arc, passes
through sodium vapour, sodium absorbs only two
yellow wavelength. Continuous spectrum with two
dark lines in the yellow region of sodium vapour is
obtained.
Band absorption spectrum
when white light is passed through the iodine
vapour, or through diluted solution of blood or through
chlorophyll or through solutions of organic and
inorganic compounds, dark bands on continuous
bright background is obtained.
5.5.3Write down Maxwell equations in integral form.
I.First equation is Gauss’s law for electricity.
Surface integral of electric field over a closed
𝟏
surface is equal to 𝜺 times the net charge inside the
𝟎
surface.
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6.2.1 What are the two conditions for total internal
reflection ?
1) light must travel from denser to rarer medium,
2) angle of incidence in the denser medium must be
greater than critical angle (i > ic).
6.2.2Why does sky appear blue?
By Rayleigh’s scattering law, intensity of light
scattered is inversely proportional to fourth power
of wavelength. violet colour which has the shortest
wavelength gets much scattered during day time. As
our eyes are more sensitive to next scattered blue
colour than violet colour the sky appears blue during
day time
6.2.3What is the reason for reddish appearance of sky
during sunset and sunrise?
During sunrise and sunset, the light from sun
travels a greater distance. By Rayleigh’s scattering,
violet colour which has the shortest wavelength gets
much scattered away and the red light of longer
wavelength reaches our eye. This is the reason for the
reddish appearance of sky during sunrise and sunset.
6.2.4Why do clouds appear white?
Clouds contains large amount of dust and
water droplets, which have size a greater than the
wavelength λ of light. In clouds all the colour’s get
equally scattered not depending on wavelength. So
clouds appear white.
6.2.5 Why sky appears dark for the astronauts
Above the atmosphere, there is no light
scattering particles. So sky appears dark for the
astronauts
6.2.6 How are rainbows formed?
electric field lines do not form a continuous closed
path. isolated positive charge or negative charge can
exist. It relates the net electric flux to net electric charge
Rainbow is formed due to dispersion of sunlight
enclosed in a surface.
through droplets of water during rainy days.
II. Second equation is Gauss’s law for magnetism
Surface integral of magnetic field over a 6.2.7 Why do stars twinkle?
Stars appear twinkling because of the refraction of
closed surface is zero.
light by movement of the atmospheric layers with
varying refractive indices, which is clearly seen in the
magnetic lines of force form a continuous closed night sky.
path. isolated magnetic monopole do not exists.
6.2.8 What is principle of reversibility?
III.Third equation is Faraday’s law of electromagnetic
Light will travel the same path if its direction
induction.
of travel is reversed.
Line integral of the electric field is equal to 6.2.9What is optical path?
the rate of change of magnetic flux around any Optical path is the distance d' travelled by light in
vacuum for the same time as it travels a distance d in
closed path.
the medium
6.2.10.State the laws of refraction.
1) Incident ray, Refracted ray and Normal are
III.Fourth equation is Ampere – Maxwell’s law
Coplanar.
Magnetic field around any closed path is
related to the conduction current and displacement 2) The ratio of sine of angle of incidence sin i in the first
medium to the sine of angle of refraction
sin r r
current through that path.
in the second medium is equal to the ratio of refractive
index of the second medium n2 to that of the refractive
index of the first medium n1
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6.2.11 What is Rayleigh’s scattering?
Intensity of light in Rayleigh’s scattering is
inversely proportional to fourth power of
wavelength.
6.2.12
What
is
critical
angle
and
total internal reflection?
The angle of incidence in the denser medium
for which the refracted ray graces the boundary is
called critical angle ic.
Complete reflection of light into the denser
medium itself, is called total internal reflection
6.3.3. Obtain the equation for critical angle.
When light passes from an optically denser
6.2.13 Give the characteristics of image formed by a
medium to an optically rarer medium, it bends away
plane mirror.
from the normal. As angle of incidence i is increased,
1) The image formed by a plane mirror is virtual, angle of refraction r increases and at a certain stage r
erect, and laterally inverted.
becomes 90°. The angle of incidence in the denser
2) The size of the image and object are same.
medium for which the refracted ray graces the
3) The distance of object and image from the mirror boundary is called critical angle ic.
are same.
By Snell’s law
6.2.14 How does an endoscope work?
An endoscope is an instrument which has bundle of
optical fibres working on the principle of total
internal reflection. It is used by doctors to see inside
of a patient’s body and do operations. The optical
fibres are inserted into the body through mouth, nose
(or) a special hole made in the body.
6.3.1 What is optical path? Obtain its equation.
Distance d' travelled by light in vacuum in the
same time as it travelled a distance d in a medium is
known as Optical path of the medium.
Light travels with a speed v through a medium 6.3.4 Obtain the equation for apparent depth.
Bottom of a tank filled with water appears to
of refractive index n and distance d in a time t. Light
be
raised
when seen from top air medium.
travels with a speed c through vacuum and distance d'
Light from the object O passes from denser
in the same time t.
medium (water) to rarer medium (air) to reach our
eyes. The refractive index of the denser medium is n1
and that of rarer medium is n2. The angle of incidence
in the denser medium is i and the angle of refraction in
the rarer medium is r. By Snell’s law
6.3.2 Derive relation between f & R for spherical mirror.
1) C is the centre of curvature of the mirror with pole
P. PF= f is focal length and PC = R is the radius
of curvature.
2) A ray of light passing parallel to the principal
axis is incident at M.
3) After reflection, it passes through the principal
focus F.
4) CM is drawn normal to the mirror and MP is the
drawn perpendicular to the principal axis.
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6.3.5 Derive the equation for effective focal length for
lenses in contact.
Two lenses of focal length f 1 and f2 are placed
coaxially in contact with each other. When Object O is
placed beyond Focus of first lens ,an image is formed
by it at I'. This image I' acts as an object for the
second lens. and the final image is formed at I by
Second Lens.
For First Lens, object distance 𝐏𝑶 = 𝒖 and image
distance 𝐏𝐈 ′ = 𝐯 ′ .For Second Lens, object distance
𝐏𝐈 ′ = 𝐯 ′ and image distance 𝐏𝑰 = 𝐯
6.5.1 Describe the Fizeau’s method to determine speed
of light.
Light from source S falls on a partially
silvered glass plate G kept at an angle of 45o to the
incident light. Light then passes through one cut of a
rotating toothed-wheel with N teeth and N cuts of
equal widths.
When wheel is not rotating, light travels a long
distance d, about 8 km, gets reflected from a mirror and
passes through the same cut and reach the eyes of the
observer.
Working: The wheel is rotated with high angular
speed ω, until light passing through one cut would
completely be blocked by the adjacent tooth. So the
observer cannot see the image of source.
Expression for speed of light:
Ɵ is the angle between one tooth and the next
slot which is turned within that time t and distance
covered by light is 2d.
6.3.6 Obtain the equation for lateral magnification of
thin lens..
An object 𝐎𝐎′ of height h1 is placed on the
principal axis perpendicular to the principal axis. The
inverted real image 𝐈𝐈 ′ of height h2 is formed.
Lateral (or) transverse magnification m is
defined as the ratio of the height of the image to
height of the object
value of speed of light determined by Fizeau was very
close to the actual value c = 2.99792 ×108 m s–1
6.5.2 Derive the mirror equation and the equation for
lateral magnification.
First paraxial light BD from the object AB gets
reflected on the concave mirror at D and passes through
the focus F.
Second light ray BP incident at the pole P is
reflected along P𝑩′ .
Third light ray BC passing through centre of
curvature C, gets reflected back along the same path.
The three reflected rays intersect at the point where
a real, inverted image 𝑨′ 𝑩′ is formed.
magnification is negative for real image and positive
for virtual image. In the case of a concave lens, the
magnification is always positive and less than one.
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This is Mirror Equation
The lateral (or) transverse magnification m is
defined as the ratio of the height of the image to the
height of the object.
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This equation is called the lens maker’s formula,
because it tells the lens manufactures what curvature
is needed to make a lens of desired focal length f with
a material of particular refractive index n.
6.5.4Derive the equation for angle of deviation in a
prism and refractive index of material of the prism.
PQ is the incident ray QR is the refracted ray and
RS is the emergent ray. 𝒊𝟏 and 𝒓𝟏 are angles of incidence
and refraction at the first face AB. 𝒊𝟐 and 𝒓𝟐 are angles
of incidence and refraction at the first face AC. The
angle between the incident ray PQ and the emergent
ray RS is called the angle of deviation d.
6.5.3 Obtain lens maker’s formula and mention its
significance.
A thin lens of refractive index 𝒏𝟐 is placed between two
medium of same refractive index 𝒏𝟏 . Let 𝑹𝟏 and 𝑹𝟐 be
the radii of curvature of two spherical surfaces 1 and 2
respectively.
Using the ray from object O, after refraction,
Surface 1 forms image at 𝑰′ . But the image at 𝑰′ acts
as object for surface 2. So surface 2 bends the ray
and forms final Image at I.
Angle of deviation decreases with increase in angle of
refraction at a spherical surface 1 when light moves incidence and reaches a minimum value called angle of
from medium of refractive index 𝐧𝟏 to 𝐧𝟐 is
minimum deviation and then continues to increase.
Refracted ray inside the prism is parallel to its base
of the prism.
Refraction at a spherical
surface 2 when light moves from medium of refractive
index 𝐧𝟐 to 𝐧𝟏 is
6.5.5 What is dispersion? Obtain the equation for
dispersive power of a medium.
Dispersion is splitting of white light into its
constituent colours. A is the angle of a small angle
prism A=100 and δ be its angle of minimum deviation.
Refractive index of prism
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Let δV, δR are the angles of deviation for violet and red
light. Let nV and nR are the refractive indices for the
violet and red light respectively.
The dispersive power ω is positive and dimensionless
quantity. It depends only on the nature of material
of the prism and not on the angle of the prism.
6.5.6 Derive the equation for acceptance angle and
numerical aperture, of optical fiber.
Light should be incident at a certain angle
called acceptance angle at the end of the optical fibre
while entering into it. At acceptance angle only,
critical angle incidence occurs in the core-cladding
boundary inside the optical fibre. i𝒂 is the acceptance
angle at the outer medium and core boundary at A.
6.5.7 Derive the equation for refraction at single
spherical surface.
𝒏𝟏 and 𝒏𝟐 are the refractive indices of two
transparent media separated by a spherical surface.
Light from O falls on the refracting surface at N. As
𝒏𝟐 > 𝒏𝟏 , light deviates towards the normal and meets
the principal axis at I where the image is formed.
If the first medium is air, then 𝒏𝟏 = 1 and for the
second medium 𝒏𝟐 = n,
6.2.15 What is dispersion?
Dispersion is splitting of white light into its
constituent colours.
7.2.1Why diffraction in sound more than light?
Wavelength of sound wave is large and
comparable to the geometry of obstacles like door,
windows and buildings. So, sounds bends through them.
But wavelength of light wave is very small and not
comparable to the geometry of obstacles. So, light
will not bend through the edges of those obstacles.
7.2.2 State Brewster’s law.
Tangent of the polarising angle of a
transparent medium is equal to its refractive index
7.2.3 State Malus’ law.
Transmitted Light intensity I from the
analyser is directly proportional to square of the
cosine of the angle θ between the transmission axis
of polariser and analyser
7.2.6.What is astigmatism? What is its remedy?
Astigmatic person cannot see all the directions
equally well. Wearing cylindrical lenses is its remedy
7.2.7 What is presbyopia?
Farsightedness arising due to aging is called
presbyopia as the aged people cannot strain their eye
more to reduce the focal length of the eye lens
7.2.8.Define Optic Axis
Inside the crystal there is a particular direction
in which both the rays travel with same velocity. This
direction is called optic axis.
7.2.9 Define wavefront
A wavefront is the locus of points which are
in the same state (or) phase of vibration.
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7.2.10 State Huygens’ principle.
1. Each point on the wavefront behaves as the
source of secondary wavelets spreading in all
directions with the speed of the wave.
2. The envelope to secondary wavelets gives the
position and shape of the new wavefront at a later
time.
7.2.11 What are coherent waves?
Two waves which have same phase or constant
phase difference, same frequency or wavelength,
same waveform and preferably same amplitude.
7.2.12Why two independent monochromatic sources
can never be coherent
Atoms while emitting light, produce change
in phase due to thermal vibrations. So waves emitted
from two sources will be of same frequency and same
amplitude, but not with same phase.
7.2.13What are Conditions for obtaining clear and broad
interference fringes?
1) Distance D between the screen and double slit
should be as large as possible.
2) Wavelength λ of light used must be as long as
possible.
3) Distance d between the two slits must be as small
as possible
7.2.15.Differentiate interference and diffraction
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7.2.19What are near point and normal focusing?
7.2.20 Why Compact Disc appear colourful?
Narrow circular tracks with widths
comparable to the wavelength of visible light are on
the read/writable shining side of CD. tracks act as
reflecting grating. Diffraction takes place after the
reflection of incident white light .
7.2.22. Why is oil immersed objective preferred in a
microscope?
For High magnification, minimum distance
between the two points on the object to be
resolved dmin should be decreased by increasing
optical path. So, objective of the microscope is
immersed into a bath containing oil of refractive
index n.
7.2.23. What are the advantages and disadvantages of a
reflecting telescope?
Advantages
1) objective mirror in reflecting telescope is polished
on one surface only.
2) Entire back of the mirror can be used for
supporting but in lens only rim can be used.
3) Mirror weight is less than lens.
7.2.16.What is Rayleigh’s criterion?
Disadvantages
Two points on an image are said to be just
Objective mirror focus the light inside the
resolved when the central maximum of one telescope tube.
diffraction pattern coincides with the first minimum 7.2.24.What are the salient features of corpuscular
of the other and vice-versa.
theory of light?
7.2.17. Differentiate resolution and magnification?
1. light is emitted as tiny, massless and perfectly
elastic particles called corpuscles.
2. reflection of light is due to the repulsion and
refraction of light is due to the attraction of the
corpuscles by the medium.
3. energy of light is the kinetic energy of corpuscles
4. sizes of the corpuscles give different colours to light
7.2.18. Differentiate polarised and unpolarised light.
7.2.25.What are the salient features of wave theory of
light?
1. light is a disturbance from a source which travels
as longitudinal mechanical waves through the
ether medium.
2. wave theory could successfully explain reflection,
refraction, interference and diffraction of light
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7.2.26 Define Polarising angle
7.3.4 State and Prove Malus’ law
The angle of incidence for which the
Transmitted light intensity I from the
reflected light is found to be plane polarised is analyser is directly proportional to the square of the
called polarising angle ip.
cosine of the angle θ between the transmission axis
7.2.27 What is interference of light?
Phenomenon of superposition of two light
waves produce increase in intensity at some points
and decrease in intensity at some other points is
called interference of light.
7.2.28.Define Diffraction?
Bending of waves around sharp edges into the
geometrically shadowed region.
7.3.1State and prove Brewster’s law
Tangent of the polarising angle is equal to refractive
index of a medium.
At the polarising angle, the reflected and the refracted
rays are perpendicular to each other.
7.3.3What are Uses of Polaroids
1. Polaroids are used to avoid glare.
2. used in holography.
3. used in liquid crystal display (LCD).
4. used to improve colour contrast in old oil
paintings.
5. used as window glasses to control the intensity of
incoming light.
6. Polarised laser beam acts as needle to read/write in
compact discs (CDs).
7.3.5 Discuss about pile of plates.
Pile of plates converts partially polarised
refracted light into plane polarised beam based on
brewster law. several plates are kept one behind the
other at an angle 𝟗𝟎𝟎 -i𝒑 with the horizontal surface.
So, light falls on these plates at i𝒑.
of polariser and analyser.
Let I0 be the intensity and a be the amplitude of the
electric vector of light transmitted by the polariser.
acosθ and asinθ are the parallel and perpendicular
components of amplitude a. Only (acosθ) component
will be transmitted by the analyser.
The intensity of light transmitted from the analyser
is proportional to the square of the component of the
amplitude transmitted by the analyser.
7.3.6 Obtain the equation for Fresnel’s distance
In diffraction, bending is not seen till the
diffracted ray crosses the width of central maximum at
a distance z from the slit. Distance upto which the ray
optics is obeyed and beyond which the ray optics is
not obeyed; but, the wave optics becomes significant
is called Fresnel’s distance.
7.3.4 Explain about compound microscope
When unpolarised light passes successively through the
plates, few parallel vibrations to the surface, present
in the refracted light, gets reflected at the succeeding
plates. Both reflected and the refracted lights are found
to be plane polarised.
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Compound microscope has two lenses. The a1 and a2 are the amplitudes of first and second wave ω
objective lens O near the object, forms a real, is the same angular frequency, and ϕ phase difference
inverted and magnified image of the object. This between them.
image acts as object for the eyepiece lens E close to the
eye. The eyepiece acts as simple microscope and
produce an enlarged and virtual image. The inverted
image formed by the objective is adjusted within the
focus of the eyepiece so that the final image is formed
nearly at infinity (or) at the near point. The final image
is inverted with respect to the object.
7.5.1 Obtain the equation for bandwidth in Young’s
double slit experiment
d is the distance between the double slits S 1
and S2. λ is the wavelength of coherent sources. D is
the distance of screen and double slits.
The mid-point of S1 and S2 is C and the midpoint of the screen O is equidistant from S1 and S2. P is
a point at a distance y from O. The waves from S1 and
S2 meet at P either in-phase or out-of-phase
depending upon the path difference δ between the
two waves. S1M is drawn ꓕ to S2P.
7.5.5 Discuss the diffraction at single slit and obtain the
condition for nth minimum
A plane wavefront falls normally on a single
slit AB of width a. The diffracted beam falls on a
screen kept at a distance D from the slit. The centre
of the slit is C. P is a point on the screen. All the light
reaching point P from different points on the slit make
an angle θ with the normal CO.
For P to be minimum intensity, slit AB is divided into
even parts, so that effect of one is cancelled by other
Above Formulas given distance of nth bright and nth
dark fringe from centre O. Bandwidth β is the
distance between any two consecutive bright (or)
dark fringes.
7.5.2 Obtain the equation for resultant intensity due to
interference of light
Two light waves from the two sources S1 and S2 are
meeting at point P.
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This is the magnification
for normal focusing.
Prove law of reflection using Huygens’ principle
Wavefront AB is incident on a reflecting plane
surface XY. When the wavelet from point B touches the
reflecting surface at 𝑩′ , the wavelet from point A would
have reached 𝑨′ .reflected wavefront 𝑨′ 𝑩′ emanates as a
plane wavefront.
As reflection happens in the same medium, the
speed of light is same before and after the reflection.
The time taken for the light to travel from B to 𝑩′ and A
to 𝑨′ are the same. distance B𝑩′ = distance A𝑨′ .
For P to be maximum intensity, slit AB is divided into
odd parts, so that one part is left uncancelled
7.5.3 Describing simple microscope, obtain equations
for magnification for near point and normal focusing.
A simple microscope is a magnifying convex
lens of small focal length. It produces an erect,
magnified and virtual image of the object. Object
must be placed within the focal length f (between the
points F and P) on one side of the lens and image is
viewed through the other side.
8.2.1 Define work function of a metal. Give its unit.
Minimum energy needed for an electron to
escape from the metal surface is called work function
of that metal. Unit: electron volt (eV)
8.2.2. What is photoelectric effect?
Ejection of electrons from a metal plate when
electromagnetic radiation of suitable frequency fall
on metal is called photoelectric effect
8.2.3. Give the definition of intensity of light with unit.
Intensity of light is equal to number of same
energy photons incident per unit area per unit time.
unit : Wm–2.
8.2.4. How will you define threshold frequency?
Minimum
frequency
above
which
This is magnification for near point focusing
photoelectrons are emitted is called the threshold
frequency.
8.2.5What is a photo cell? Mention the different types
of photocells.
Photo electric cell converts light energy into
electrical energy. Its Types are
1) Photo emissive cell
2) Photo voltaic cell
3) Photo conductive cell.
8.2.6. State de Broglie hypothesis.
Waves are associated with all moving
angular magnification is defined as the ratio of angle θi
elementary
particles like electrons, protons,
subtended by the image with aided eye to the angle
neutrons.
θ subtended by the object with unaided eye.
0
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8.2.7. Why we do not see the wave properties of a
baseball?
Wave nature of matter is applicable for
microscopic atomic level but really negligible for the
macroscopic baseball.
8.2.8. A proton and electron have same kinetic energy.
Which one has greater de Broglie wavelength.
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electron is called Bremsstrahlung or braking
radiation
8.2.17 Differentiate Continuous and Characteristic Xray
Spectra
De Broglie wavelength is inversely
proportional to square root of mass. Mass of electron
is lesser than mass of proton. So Electron has
Greater De Broglie wavelength.
8.2.9An electron and an alpha particle have same kinetic
energy. How are the de Broglie wavelengths related?
De Broglie wavelength is inversely
proportional to square root of mass. Mass of electron
is lesser than mass of alpha particle. So Electron has
Greater De Broglie wavelength than Alpha particle.
8.2.10 What are types of Electron emission
1.Thermionic Emission
2.Field Electric Emission
3.Photo Electric Emission
4.Secondary Emission
8.2.11 Define Stopping potential
Minimum Negative Potential given to Anode
to stop Most Energetic Electron is called Stopping
potential.
8.2.12 What are the applications of X-rays
1. X-rays are used to detect fractures
2. X-rays are used to cure skin diseases, tumors
3. X-rays are used to check for flaws in welded joints.
4. X-ray diffraction is used to study the structure of
atoms and molecules in crystals.
8.2.13Why do metals have a large number of free
electrons?
In metals, Even at room temperature, the
electrons in the outer most shells are loosely bound
to the nucleus. So,large number of free electron move
inside the metal in a random manner.
8.2.14. What is surface barrier?
The potential barrier which prevents free
electrons from leaving the metallic surface is called
surface barrier.
8.2.15 Mention the two features of x-ray spectra, not
explained by classical electromagnetic theory.
1. For a given accelerating voltage, the minimum
wavelength or cut-off wavelength of continuous x-ray
spectra is same for all targets.
2. The intensity of x-rays is significantly increased at
certain well-defined wavelengths.
8.2.16 what is Bremsstrahlung?
Interaction between fast moving electron and the
nucleus changes the path of electron by changing speed
of electron. Radiation produced by decelerating
8.3.1 List out the laws of photoelectric effect.
1.Minimum frequency above which photoelectrons
are emitted is called the threshold frequency.
2.Instantaneous Process .There is no time gap between
incidence of light and ejection of photoelectrons.
3.Number of photoelectrons and Saturation current
emitted is directly proportional to the intensity of
the incident light.
Maximum kinetic energy of the photo electrons is
directly proportional to the frequency of incident
light but does not depend on Intensity of Incident
Light.
8.3.2What are the uses of Photoelectric Cells
1. Photo cells are used as switches and sensors.
2. Street lights are Automatically turned on when it
gets dark using photocells.
3. Sounds are reproduced in motion pictures using
Photocells.
4. Athlete’s speed is measured using photocells.
5. Light intensity can be measured using Photocells.
8.3.3 Derive an expression for de Broglie wavelength
8.3.5 Write the Characteristics of photons
1. Energy of photons of frequency ν: E=hυ
2. Photons travel with the velocity of light and its
momentum is p=hν/c
3. Photons are electrically neutral, Photons are
unaffected by electric and magnetic fields.
4. When a photon interacts with matter, the total
energy, total linear momentum and angular
momentum of photon are conserved. Number of
photons may not be conserved
5. Energy of a photon is determined by the
frequency of the radiation and not by its intensity.
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8.3.4 Derive an expression for de Broglie wavelength
for electron
An electron of mass m is accelerated through a
potential difference of V volt. The kinetic energy K of
the electron is equal to electrostatic potential energy
Ve.
8.3.6 Give the construction and working of photo
emissive cell.
Photo electric cell converts light energy into
electrical energy. Two metallic electrodes, a cathode
and an anode are fixed in an evacuated glass or
quartz bulb. Semi-cylindrical cathode C is coated with
a photo sensitive material. The anode A is a thin rod or
wire. A potential difference is applied between the
anode and the cathode through a galvanometer.
8.3.7 Explain why photoelectric effect cannot be
explained on the basis of wave nature of light.
According to wave theory, light of greater
intensity should impart greater kinetic energy to the
ejected electrons. But, maximum kinetic energy of
the photoelectrons emitted does not depend on the
intensity of the incident light.
According to wave theory, even if light of low
frequency is incident on the surface, electrons should
be ejected. But, photoelectric emission is not possible
below a certain minimum frequency.
According to wave theory, electron needs large
time to get liberated from the surface to overcome
the workfunction. But, photoelectric emission is an
instantaneous process.
Therefore, the wave theory fails to explain the
existence of threshold frequency
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How do we obtain characteristic x-ray spectra?
X – ray line spectrum showing narrow peaks
at some well – defined wavelengths is called
characteristic x – ray spectrum. This spectrum is due
to the electronic transitions within the atoms, when the
target is hit by fast electrons.
When an energetic electron knocks some of
the K-shell electrons, vacancy is created. Electrons
from outer orbits jump to fill up the vacancy in the
K-shell. Energy difference between the levels is given
out in the form of x– ray photon of definite
wavelength. Such definite wavelengths, are the
characteristic of the target .
K-series in the x-ray spectrum of an element arises
due to the electronic transitions from L, M, N, . .
levels to the K-level.
Longer wavelength L-series in the x-ray spectrum of
an element arises due to the electronic transitions
from M, N, . . levels to the L-level and so on.
8.5.1.Derive Einstein’s photoelectric equation
When a photon of energy hν is incident on a
metal surface, it is completely absorbed by a single
electron and the electron is ejected.
From the law of conservation of energy
This is Einstein Photoelectric Equation.
If the electron does not lose energy by internal
collisions, then electron is emitted with maximum
kinetic energy 𝑲𝒎𝒂𝒙 .
A graph between 𝑲𝒎𝒂𝒙 of the photoelectron and
frequency ν of the incident light is a straight line.The
slope of the line is h and its y-intercept is −𝝓𝟎
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8.5.2 Explain the working of Electron Microscope
the image of the sample.
6.Magnified image is obtained on the screen by
magnetic objective projector lens system.
Electron microscope is used in all branches of science.
8.5.3.Describe briefly Davisson – Germer experiment
which demonstrated the wave nature of electrons.
Davisson and Germer demonstrated that
electron beams incident on crystals are diffracted off
in certain specific directions.
1. Electrons are emitted from the hot filament by
thermionic emission.
2. Electrons are accelerated due to the potential
difference of high tension (H.T.) battery between
the filament and the anode aluminium cylinder.
3. After passing through, two thin aluminium
diaphragms electron beam strike Nickel crystal.
4. Intensity of electrons scattered by Ni atoms in
different directions are measured by the electron
detector.
5. Angle θ between the incident beam and the scattered
beam can be changed by rotating detector.
6. A graph is plotted for intensity of the scattered
electron beam and angle θ.
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8. Knowing the value of interplanar spacing of Nickel,
the wavelength of the electron wave was
experimentally calculated as 1.65 A0.
9. wavelength calculated by de Broglie relation
forV=54 V agrees
with calculated value.
8.5.4 Explain the effect of potential difference on
photoelectric current
Frequency and intensity of the incident light
falling on cathode C are kept constant. When potential
of anode A is increased, photocurrent increases and
reaches a saturation current at which all the
photoelectrons from C are collected by A.
When a negative potential is applied to A with
respect to C, the current does not immediately drop
to zero. Photoelectrons overcomes the retarding electric
field and reach the electrode A. When the negative
potential of A is increased, Photocurrent becomes
zero at a particular negative potential V0, called
stopping or cut-off potential. kinetic energy of the
fastest electron is equal to the work done by the stopping
potential. Minimum Negative Potential given to
Anode to stop Most Energetic Electron is called
Stopping potential
7. For accelerating voltage V=54V, the scattered
wave shows a peak at an angle of 50° . Rise in
intensity is due to the constructive interference of
electrons diffracted from various atomic layers
of the target material.
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4) Very few alpha particles returned back (back
scattered) –that is, deflected back by 180°
9.2.1.Define impact parameter.
Perpendicular distance between the centre of 9.2.10 Give the conclusions of Rutherford alpha
the gold nucleus and the direction of alpha particle scattering experiment
velocity vector when alpha particle is at a large 1) Nucleus is positively charged tiny sphere of radius
10-14m.
distance is called impact parameter.
2) Nucleus is surrounded by circulating negatively
9.2.2Define curie.
charged electrons.
1 Curie = 3.7 x 1010 decays per second =3.7 x 1010Bq
9.2.11Write down the postulates of Bohr atom model.
9.2.3 In alpha decay, why the unstable nucleus
1) Coulomb electrostatic force of attraction between
emits24He nucleus? Why it does not emit four separate
electron and nucleus provides centripetal force
nucleons?
for electron to revolve around the nucleus.
In any decay process, the conservation of
2) Angular momentum of the electron in the
energy, conservation of linear momentum and
stationary orbits is an integral multiple of h/ 2π.
conservation of angular momentum must be obeyed.
3) An electron can jump from one orbit to another
If Four separate nucleons are emitted then
orbit by absorbing or emitting a photon whose
Disintegration energy becomes negative. So the total
energy is equal to the difference in energy (ΔE)
mass of products is greater than that of parent
between the two orbital levels.
nucleus. This kind of process cannot occur in nature.
9.2.12 Write down the draw backs of Bohr atom model.
9.2.4 Define atomic mass unit u.
th
One atomic mass unit (u) is defined as the 1/12 of the 1) Bohr atom model is valid only for hydrogen atom
but not for complex atoms.
mass of carbon isotope 𝟏𝟐𝟔𝑪. 𝟏𝒖 = 𝟏. 𝟔𝟔 𝐱 𝟏𝟎−𝟐𝟕 𝒌𝒈
2) Fine structure of hydrogen spectrum is not
9.2.5 Show that nuclear density is constant for nuclei
explained by Bohr atom model.
with Z > 10.
3) Intensity variations in the spectral lines is not
explained by Bohr atom model.
4) Distribution of electrons in atoms is not
completely explained by Bohr atom model.
9.2.13What is meant by excitation energy.
Energy required to excite electron from lower
Nuclear density is independent of the mass number
energy state to higher energy state is called excitation
A. So, all the nuclei with Z > 10 have the same density
energy.
9.2.6What is mass defect?
9.2.14 Define the ionization energy and ionization
Difference in expected mass and experimental potential.
mass of nucleus is called mass defect
Minimum energy required to remove an
9.2.7What is binding energy of a nucleus?
electron from the atom in ground state is called
Energy equivalent to Mass defect and binds ionization energy. Ionization energy per unit charge
the nucleons inside the nucleus is called binding is called ionization potential.
9.2.15 Calculate the energy equivalent of 1 atomic mass
energy of nucleus.
unit.
𝒖 = 𝟏. 𝟔𝟔 𝐱 𝟏𝟎−𝟐𝟕 𝒌𝒈
9.2.8 What is distance of closest approach?
2
-27
8 2
Minimum distance between the centre of the E = mc = 1.66x10 x (3x 10 )
nucleus and the alpha particle just before the alpha
𝟏𝟒.𝟗𝟒 𝐱 𝟏𝟎 −𝟏𝟏
= 𝟏𝟒. 𝟗𝟒 𝐱 𝟏𝟎−𝟏𝟏 J =
𝒆𝑽
𝟏.𝟔 𝐱 𝟏𝟎 −𝟏𝟗
particle gets reflected back through 180° is the
distance of closest approach.
= 𝟗𝟑𝟏𝑴𝒆𝑽
9.2.9 Give the results of Rutherford alpha scattering
experiment.
1) Most of the alpha particles were un-deflected
through the gold foil and went straight.
2) Some of the alpha particles were deflected
through a small angle.
3) A few alpha particles (one in thousand) were
deflected through the angle more than 90°
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9.3.1. Write the properties of cathode rays.
1) Cathode rays ionize the gas.
2) They affect photographic plates
3) They produce fluorescence on certain crystals .
4) They produce heat while falling on matter.
5) They are deflected by electric and magnetic field.
6) They possess energy and momentum.
7) They travel in a straight line with high speed of the
order of 107m s-1.
8) When the cathode rays fall on a material of high
atomic weight, x-rays are produced.
9.3.2 Discuss the spectral series of hydrogen atom.
In a hydrogen atom, when electrons jump back from
excited state (m) to lower state (n), radiations ie.,
spectral lines are emitted. Spectral lines of hydrogen are
grouped in separate series.𝝂
̅ is the wave number of a
spectral line which is inverse of wavelength, R is the
Rydberg constant whose value R= 1.09737 × 107 m-1
9.3.4 Explain in detail the nuclear force
1. Attractive force which holds the nucleus together
is called strong nuclear force.
2. Nuclear force is the strongest force in nature.
3. Strong nuclear force is attractive only
4. Magnitude of nuclear force is same for protonproton, proton-neutron, and neutron – neutron.
5. Nuclear force does not act on electrons.
9.3.5 Discuss the properties of neutrino
1) neutrino has zero charge
2) It has an antiparticle called anti-neutrino.
3) neutrino has very small mass.
4) It interacts very weakly with the matter. So, it is
very
difficult
to
detect
it.
neutrinos coming from the sun, passes through
our body without causing interaction.
5) Neutrino is emitted in the beta decay process
carrying away missing energy and momentum
9.3.6 Explain the idea of carbon dating.
Using carbon dating technique based on beta
decay, the age of an ancient object can be calculated.
All living organisms absorb carbon dioxide (CO2) from
air to synthesize organic molecules. Absorbed CO2
contains very small fraction (𝟏. 𝟑 𝐱 𝟏𝟎−𝟏𝟐 ) of
radioactive 𝟏𝟒𝟔𝐂. half-life of 𝟏𝟒𝟔𝐂 is 5730 years.
𝟏𝟒
𝟔𝐂 in the atmosphere is always decaying but it is
produced continuously due to cosmic rays from outer
space. ratio of 𝟏𝟒𝟔𝐂 to 𝟏𝟐𝟔𝐂 in the living organism is also
nearly constant. But when the organism dies, it stops
absorbing CO2 and 𝟏𝟒𝟔𝐂 decays.
By knowing the ratio of 𝟏𝟒𝟔𝐂 to 𝟏𝟐𝟔𝐂 in the dead matter,
9.3.3.Discuss the alpha , beta and gamma decay process the age of the specimen can be calculated.
9.3.7 Derive the expression for distance of closest
approach?
When an alpha particle moves straight towards
gold nucleus, it reaches a point where it comes to rest
momentarily and returns back. Minimum distance
between the centre of the nucleus and the alpha
particle just before the alpha particle gets reflected
back through 180° is the distance of closest approach
𝒓𝟎 .
Using 𝒓𝟎 ,Rutherford calculated the radius of the nucleus
for different nuclei ranging from 𝟏𝟎−𝟏𝟒 𝒎 to𝟏𝟎−𝟏𝟓 𝒎.
size of the nucleus is always lesser than the distance of
closest approach.
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9.5.1 Explain the J.J. Thomson experiment to determine
the specific charge of electron.
Principle: cathode rays are deflected by electric and
magnetic fields.
In a highly evacuated discharge tube, cathode
rays (electron beam) produced at cathode, are
attracted towards anode disc A. By passing through
pin hole in Anode disc, cathode rays are made into
narrow beam.
cathode rays pass through the parallel metal
plates which are maintained at high voltage. Using
pole pieces of magnet, magnetic field is produced. Both
electric and magnetic fields are acting perpendicular
to each other. When the cathode rays strike the
screen coated with zinc sulphide, due to scintillation,
a bright spot is observed.
Determination of velocity of cathode rays
For a fixed electric field between the plates, the
magnetic field is adjusted such that the magnitude of
magnetic force is balanced by the magnitude of
electric force.
Determination of specific charge of electron
Let V be the potential difference between anode and
cathode and e be the charge of electron. Then from law
of conservation of energy,
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𝑵𝟎 is the number of nuclei present in the radioactive
sample at time t = 0 s. N is the number of undecayed
nuclei present at any time t. By integrating
Number of atoms is decreasing exponentially over
the length of time. Time taken for all the radioactive
nuclei to decay will be infinite.
9.5.3Derive the energy expression for an electron is
the hydrogen atom using Bohr atom model.
1) Angular momentum of the electron in the
stationary orbits is an integral multiple of h/ 2π.
2) An electron can jump from one orbit to another
orbit by absorbing or emitting a photon whose
energy is equal to the difference in energy (ΔE)
between the two orbital levels.
9.5.2 Obtain the law of radioactivity.
At any instant t, the number of radioactive decays
per unit time, is proportional to the number of nuclei
at the same instant. dN is the number of nuclei decayed in
the time interval dt, then
9.5.4 Derive the expression for radius of nth orbit in the
hydrogen atom using Bohr atom model.
Let Z be the atomic number of the atom, then
+Ze is the charge of the nucleus. – e is the charge of
the electron.
λ is the decay constant of the radioactive element.
Negative sign indicates that N is decreasing.
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down with constant velocity. viscous force and
buoyant force balance the gravitational force
n is the principal quantum number
Determination of electric charge
When the electric field is switched on, charged
oil drops accelerates upward due to electric force.
charged oil drop is kept stationery by adjusting
electric field.
smallest radius 𝒓𝟏 = 𝟎. 𝟓𝟐𝟗 𝑨𝟎 of the orbit in hydrogen
atom is called bohr radius. Write Bohr’s Postulates if asked
1) Angular momentum of the electron in the
stationary orbits is an integral multiple of h/ 2π.
3) An electron can jump from one stationery orbit to
another orbit by absorbing or emitting a photon
whose energy is equal to the difference in energy
(ΔE) between the two orbital levels.
9.5.5 Discuss the Millikan’s oil drop experiment to
determine the charge of an electron.
Two horizontal plates A & B of diameter 20cm
are separated by 1.5cm. A potential difference of 10kV
is applied to the plates. Fine drops of highly viscous oil
falls through a hole H in the plate A due to gravity. Due
to ionization of air by X-rays, Oil drops acquire charge.
charged oil droplets can be made to move up or down
or remain rest. ρ be the Density of oil, σ is the Density
of air, r I s the radius of oil drop, η is the Coefficient of
viscosity of air.m be the mass of the oil drop and q be its
charge. forces acting on the droplet are
Millikan repeated this experiment several times and
found that the charge of any oil drop can be written as
integral multiple of a basic value, which is nothing but
the charge of an electron (1.6 x 10-19C).
9.5.6 Describe the working of nuclear reactor with a
block diagram.
Nuclear reactor is a device in which the
nuclear fission takes place in a self-sustained
controlled manner. Energy produced is used either for
research purpose or for power generation. The main
parts of a nuclear reactor are
1. Fuel
2. Moderator
3. Control rods
4. Cooling system
5. Shielding
Fuel: Fissionable material such as uranium or
plutonium is used as fuel. Naturally occurring uranium
𝟐𝟑𝟖
contains only 0.7% of 𝟐𝟑𝟓
𝟗𝟐 𝑼 and 99.3% of 𝟗𝟐 𝑼 . So
𝟐𝟑𝟖
𝟐𝟑𝟓
𝟗𝟐 𝑼 must be enriched to have 2% to 4% of 𝟗𝟐 𝑼 . A
mixture of beryllium with plutonium or polonium is
used as the neutron source, to initiate the chain
reaction for the first time.
Moderators: The moderator is used to convert fast
neutrons into slow neutrons. Heavy water (D2O) and
graphite are used as moderators. moderators are very
Determination of radius of the droplet
When the electric field is switched off, the oil light nuclei having mass comparable to that of neutrons.
drop accelerates downwards. Due to air drag forces, the light nuclei undergo collision with fast neutrons and the
oil drops easily attain its terminal velocity and moves speed of the neutron is reduced.
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Control rods: The control rods are used to adjust the
reaction rate. cadmium or boron acts as control rod
material are inserted into the uranium blocks. On an
average 2.5 neutrons are emitted per fission. To have the
controlled chain reactions, only one neutron is allowed
to cause another fission and the remaining neutrons are
absorbed by the control rods.
If the average neutrons produced per fission is equal
to one, then reactor is said to be in critical state. If it
is greater than one, then reactor is said to be in supercritical and it may explode sooner. So, all the nuclear
reactors are maintained in critical state by suitable
adjustment of control rods
Cooling system: The cooling system removes the heat
generated in the reactor core. Ordinary water, heavy
water and liquid sodium are used as coolant since
they have very high specific heat capacity and have
large boiling point under high pressure. This coolant
passes through the fuel block and carries away the
heat to the steam generator through heat exchanger.
The steam runs the turbines which produces
electricity in power reactors.
Shielding: For a protection against harmful radiations,
the nuclear reactor is surrounded by a concrete wall
of thickness of about 2 to 2.5 m.
9.5.7 Explain the variation of average binding energy
with the mass number using graph and discuss about its
features.
The binding energy per nucleon ̅̅̅̅
𝑩𝑬 is the
energy required to separate single nucleon from the
particular nucleus. Graph is plotted by taking A
along X-axis and ̅̅̅̅
𝑩𝑬 is taken along Y-axis
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1. As the mass number increases, the value of ̅̅̅̅
𝑩𝑬
rises until it reaches a maximum value of 8.8
MeV for A = 56 (iron) and then it slowly
decreases.
2. The average binding energy per nucleon is about
8.5 MeV for nuclei having mass number lying
between A = 40 and 120. These elements are
comparatively more stable and not radioactive.
3. For higher mass numbers, the ̅̅̅̅
𝑩𝑬 decreases
slowly ie., curve drops slowly. ̅̅̅̅
𝑩𝑬 for uranium is
about 7.6 MeV. Such nuclei are unstable and
exhibit radioactive.
4. If two light nuclei with A<28 combine to form a
nucleus with A<56, the binding energy per
nucleon is more for final nucleus than initial
nuclei. A large amount of energy will be released.
This process nuclear fusion occurs in hydrogen
bomb.
5. If a nucleus of heavy element is split (fission) into
two or more nuclei of medium value A, a large
amount of energy will be released. This
uncontrolled process nuclear fission occurs in
atom bomb.
9.5.8 Discuss the process of nuclear fusion and how
energy is generated in stars ?
When the surrounding temperature reaches
around 107K, two or more light nuclei having mass
number (A<20) combine to form a heavier nucleus,
is called nuclear fusion. In the nuclear fusion, the mass
of the resultant nucleus is less than the sum of the
masses of original light nuclei. The mass difference
appears as energy. To overcome coulomb repulsive
force between two light positive nuclei, high
temperature 107K is needed.
In most of the stars like Sun, hydrogen atoms
fuse into helium and in some stars helium atoms fuse
into heavier elements to release nuclear fusion
energy.
The sun’s interior temperature is around 1.5
x 107K. In sun, 6×1011kg of hydrogen is converted into
helium every second. sun has enough hydrogen such
that these fusion reactions last for another 5 billion
years. When the hydrogen is burnt out, the sun will
enter into new phase called red giant where helium
will fuse to become carbon. During this stage, sun will
expand greatly in size and all its planets will be engulfed
in it. According to Hans Bethe, the sun is powered by
3 step proton-proton cycle of fusion reaction. overall
energy produced in the fusion reactions of sun is
about 27 MeV.
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9.5.9 Explain J.J. Thomson experiment to determine the
specific charge of electron by switching off magnetic
field. (Another method)
Principle: cathode rays are deflected by electric and
magnetic fields.
In a
highly evacuated discharge tube,
cathode rays (electron beam) produced at cathode,
are attracted towards anode disc A. By passing
through pin hole in Anode disc, cathode rays are made
into narrow beam.
cathode rays pass through the parallel metal
plates which are maintained at high voltage. After
passing through two parallel metal plates, cathode rays
strike the screen coated with zinc sulphide. Due to
scintillation, a bright spot is observed.
Determination of velocity of cathode rays By
connecting parallel metal plates to high voltage, Electric
field E is produced. Using pole pieces of magnet,
magnetic field B is produced. Electric and magnetic
field act right angles to each other. They are adjusted
so that deflection produced by magnetic field force is
cancelled by deflection produced by electric field
force.
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9.3.8 What is half life and mean life of a radio active
nucleus? Give the expression.
Half-life (𝑻𝟏/𝟐 ) time of a radioactive nucleus is
the time required for half the number of atoms to
disintegrate from its initial value.
Mean life (τ): Mean life time (𝛕) of a radioactive
nucleus is the ratio of sum or integration of life times
of all nuclei to the total number of nuclei present
initially. Actual life time for each radioactive nucleus
varies from zero to infinity.
9.3.9 Briefly explain the elementary particles present in
nature.
Protons and neutrons are not fundamental
particles. They are made up of elementary particles
called quarks. Electrons are fundamental or elementary
particles because they are not made up of anything.
There are six quarks namely, up, down, charm,
strange, top and bottom and their antiparticles. All
quarks have fractional charges. charge of up quark
𝟐
𝟏
is + 𝒆 and down quark is − 𝒆.
𝟑
𝟑
According to quark model, proton is made up of two
up quarks and one down quark and neutron is made
up of one up quark and two down quarks
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10.Electronics and communication
10.2.1Distinguish between intrinsic and extrinsic
semiconductors.
10.2.2. Why is temperature co-efficient of resistance
negative for semiconductor?
For a semi conductor, when temperature
increases, electrical conduction increases and
resistance decreases. So, temperature co-efficient of
resistance is negative for semiconductor.
10.2.3What do you mean by doping?
Process of adding impurities to intrinsic semi
conductor is called doping.
10.2.4Distinguish between avalanche and Zener
breakdown.
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10.2.10.How electron-hole pairs are created in a
semiconductor material?
When an electron is excited, covalent bond is
broken. Each excited electron leaves a vacancy(hole)
to complete bonding to satisfy Octet rule. So,
electron-hole pairs are created.
10.2.11. Define barrier potential.
Difference in potential across the depletion
layer of P-N junction diode is called the barrier
potential 𝑽𝒃. At 250C, barrier potential is
approximately 0.7 V for silicon and 0.3 V for
germanium.
10.2.12. What is meant by biasing? Mention its types.
Providing external energy(voltage) to charge
carriers to overcome the barrier potential and make
them move in a particular direction is known as
biasing. Types : 1. Forward bias 2. Reverse bias
10.2.13 what are the types of biasing
Forward bias
If the positive terminal of the external voltage
source is connected to the p-side and the negative
terminal to the n-side, it is called forward bias
Reverse bias
If the positive terminal of the battery is
connected to the n-side and the negative terminal to
the p-side, the junction is said to be reverse biased
10.2.14. What is an integrated circuit?
An integrated circuit (IC) is a chip or microchip,
consisting of thousands to millions of transistors,
resistors, capacitors, etc. integrated on a small flat
piece of Silicon, a semiconductor material.
10.2.15. What is modulation?
For long distance transmission, the low
frequency input baseband signal is superimposed
onto a high frequency radio signal by a process
called modulation.
10.2.16 Define Bandwidth
The frequency range over which the
baseband signals or the information signals such as
voice, music, picture, etc. is transmitted is known as
bandwidth.
10.2.17 Explain centre frequency or resting frequency
in frequency modulation.
Normal frequency of a carrier wave which
does not change when frequency of baseband signal
is zero is known as centre frequency or resting
frequency. Practically this is the allotted frequency of
the FM transmitter.
10.2.18 What are the advantages of ICs
10.2.5A diode is called as a unidirectional device. Why
A diode conducts current by giving small
resistance when it is forward biased. But it does not
conduct current when it is reverse biased due to very
large resistance.
10.2.6What do you mean by leakage current in a diode?
Under reverse bias, a very small current in
μA, flows across the PN junction. This current due
to the flow of the minority charge carriers is called
leakage current.
10.2.7Why NOR & NAND called universal gates?
NAND and NOR gates are known as universal
gates because any other logic gate can be made from
NAND or NOR gates.
10.2.8. What is rectification?
The process in which alternating voltage or
alternating current is converted into direct voltage
or direct current is known as rectification.
10.2.9. Why can’t we interchange the emitter and
collector in a transistor made of same semiconductor
material?
Because of the differing size and the amount of
Low cost, High performance with speed,
doping, the emitter and collector cannot be
Small size, and Large capacity of chips.
interchanged.
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10.2.19 Define forbidden energy gap.
Energy gap between the valence band and the
conduction band is called forbidden energy gap (Eg).
10.2.20 What are the Applications of Zener Diode
Zener diode is used
1) as voltage regulator
2) for calibrating voltages
3) to provide fixed reference voltage in a network for
biasing
4) to protect of any gadget against damage from
accidental application of excessive voltage.
10.3.1 What is Amplitude modulation? Explain
with necessary diagrams.
Amplitude of the carrier signal is modified
according to the instantaneous amplitude of the
baseband signal is called Amplitude modulation.
Amplitude modulation is used in radio and TV
broadcasting. Carrier wave is modified in proportion to The frequency of the modulated wave decreases
when the amplitude of the baseband signal increases
the amplitude of the baseband signal.
in the negative direction(B, D).
10.5.1. State and prove De Morgan’s 1 & 2 theorems.
First Theorem: Complement of the Sum of two
inputs is equal to the Product of its Complements.
Second Theorem: Complement of the Product of two
inputs is equal to the Sum of its Complements.
10.3.2 What is frequency modulation? Explain with
necessary diagrams.
Frequency of the carrier signal is modified
according to the instantaneous amplitude of the
baseband signal is called frequency modulation.
When the amplitude of the baseband signal is
zero in, the frequency of the modulated signal is the same
as the carrier signal known as Resting frequency
The frequency of the modulated wave
increases when the amplitude of the baseband signal
increases in the positive direction (A, C).
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10.5.2Explain the working of a half wave rectifier
is zero potential. The diode D1 is forward biased and
diode D2 is reverse biased. Diode D1 conducts
current along MD1ABC. The current flows through
RL and output voltage V0 is developed across RL.
During the negative half of AC cycle terminals
N is positive potential M is negative potential and C
is zero potential. The diode D2 is forward biased and
diode D1 is reverse biased. Diode D2 conducts
current along ND2ABC. The current flows through 𝑹𝑳
In a half wave rectifier circuit, Only one half of the
in the same direction and output voltage V0 is developed
input AC wave is rectified while the other half is
across 𝑹𝑳 .
blocked.
It consists of pn junction diode D, a transformer and
load Resistance RL
During the positive half of AC cycle, terminal A
becomes positive with respect to terminal B. The
diode is forward biased and hence it conducts. The
current flows through 𝑹𝑳 and output voltage 𝑽𝟎 is
developed across 𝑹𝑳 .
During the Negative half of AC cycle, terminal A
becomes negative with respect to terminal B. The Steady voltage is obtained with the help of filter circuits
diode is reverse biased and hence it does not conduct and voltage regulator circuits.
current. No output voltage V0 is developed across 𝑹𝑳 .
Efficiency (η) is the ratio of the output dc
Steady voltage is obtained with the help of filter circuits power to the input ac power. For half wave rectifier
and voltage regulator circuits.
ƞ= 81.2 %
Efficiency (η) is the ratio of the output dc power to
the input ac power. For half wave rectifier ƞ= 40.6 %
10.5.3 Explain the construction and working of a full
wave rectifier.
In a Full Wave rectifier both positive and negative half
cycles of the AC input signal is rectified.
It consists of two p-n junction diodes D1, D2, a center
tapped transformer and load Resistance RL.
10.5.4 Explain the formation of depletion region and
barrier potential in PN junction diode.
1) p-n junction is formed when a semiconductor
crystal is doped such that its one side is p-type
semiconductor and the other side is n-type
semiconductor
2) Whenever p-n junction is formed, some of the free
electrons diffuse from the n-side to the p-side
while the holes from the p-side to the n-side.
3) The diffusion of the majority charge carriers
across the junction gives rise to an electric
current, called diffusion current.
4) When an electron leaves the n-side, a pentavalent
atom in the n-side becomes a positive ion.
5) The free electron moving into p-side recombines
with a hole present in a trivalent atom near the
junction and the trivalent atom becomes a negative
ion.
During the positive half of AC cycle terminals
M is positive potential N is negative potential and C
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6) The thin region near the junction which is free
from charge carriers (free electrons and holes)
and has immobile ions on both sides is called
depletion region.
7) Immobile ions on both sides establish an electric
potential difference across the junction.
8) If the free electron from n-side has enough energy,
it can break through the potential difference wall
and enter into the p-region. Then, it can recombine
with a hole and create another negative ion.
9) The strength of the electric potential difference
across the depletion region keeps on increasing with
each electron crossing.
10) A equilibrium is reached when the internal repulsion
of the depletion layer stops further diffusion of free
electrons across the junction.
11) This difference in potential across the depletion
layer is called the barrier potential 𝑽𝒃 . At 𝟐𝟓𝟎 C,
this barrier potential is 0.7 V for silicon and 0.3 V
for germanium.
10.5.5 Transistor functions as a switch. Explain
Transistor functions like an electronic switch,
that helps to turn ON or OFF a given circuit by a small
control signal. Signal keeps the transistor in
saturation region making it as a closed switch or in
cut-off region, making it as an open switch.
When the input is low:
1) When the input signal voltage is low (say 0V), the
base current 𝑰𝑩 is zero and transistor is not
properly forward biased. It is in cut off region.
2) So, collector current is zero and voltage drop
across 𝑹𝑪 is nearly zero. The output voltage is
high and is equal to 𝑽𝑪𝑪 .
3) As no current flows through the transistor, it is
in switched off state. The transistor acts as an
open switch.
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3) As maximum current flows through the
transistor, it is in switched on state. The
transistor acts as a closed switch.
A high input to the transistor gives a low output and a
low input gives a high output. output voltage is
opposite to the applied input voltage. Therefore, a
transistor can be used as an inverter (NOT gate).
11.Recent developments in physics
11.2.1Why steel is preferred in making Robots?
Steel is several times stronger. Due to the inherent
strength of metal, robot bodies can be made using sheet,
bar, rod, channel, and other shapes.
11.2.2What are black holes?
Black holes are the end stage of stars.They are highly
dense massive object. It has very strong gravitational
force such that no particle even light can escape from it.
11.2.3Mention any two advantages and disadvantages
of Robotics.
Advantages:
1. Robots are much cheaper than humans.
2. Robots never get tired like humans.
3. Stronger and faster than humans.
4. Robots can work in extreme hot or cold, space or
underwater.
Disadvantages:
1. Robots have no sense of emotions or conscience.
2. They lack empathy and hence create an
emotionless workplace.
3. Unemployment problem will increase.
11.2.4 What is the difference between Nano materials
and Bulk materials?
1. Size of particle in Nano Materials is less than
100nm.
Size of particle in Bulk Materials is greater than
100nm.
2. Properties of the same material in Nano form and
Bulk Form are different
11.2.5 What are the components of Robots?
1. Controller -brain :Controller run by a computer
gives commands for the moving parts to perform the
job.
2. Mechanical parts - motors, pistons, grippers,
wheels, and gears that make the robot move, grab,
turn, and lift.
3. Sensors - to tell the robot about its surroundings.
When the input is high:
It helps to determine the sizes and shapes of the objects
1) When the input signal voltage is increased to high around, distance between the objects, and directions as
value (say +5 V), the base current 𝑰𝑩 increases well.
and transistor is properly forward biased. It is in 11.2.6What are the types of ROBOTS
saturation region.
1.HUMAN ROBOT: Certain robots are made to resemble
2) So, collector current 𝑰𝑪 increases and voltage humans in appearance and replicate the human activities like
lifting, and sensing, etc
drop across 𝑹𝑪 increases. output voltage is close walking,
2.INDUSTRIAL ROBOTS
to zero (since 𝑽𝟎 = 𝑽𝑪𝑪 – 𝑰𝑪 𝑹𝑪).
Six main types of industrial robots
1.Cartesian 2. SCARA 3.Cylindrical 4.Delta 5.Polar
6.Vertically articulated
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