Assignment
CBSE XII
PHYSICS (Chapter-1)
ELECTRIC CHARGES AND FIELDS
TWO Marks Questions
1. Two charges +Q and –Q are kept at (–x2 0) and (x1, 0) respectively in the X-Y plane. Find the
magnitude and direction of the net electric field at the origin (0, 0).
THREE Marks Questions
1. State Gauss’s law in electrostatics. Use gauss’s law to derive an expression for the electric field
due to a long straight wire of linear charge density C-m.
FIVE Marks Questions
1. (i) Define electric flux. Write its SI unit.
(ii) The electric field components due to a charge inside the cube of side 0.1 m are shown
E x  x,
Where,   500 N / C-m
E y  0, E z  0
Calculate
(a) the flux through the cube and
(b) the charge inside the cube.
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PHYSICS(Chapter-2)
Electrostatic Potential &Capacitance
TWO Marks Questions
1. Two identical parallel plate (air) capacitors C1 and C2 have capacitance C each. The space between their
plates is now filled with dielectrics as shown. If the two capacitors still have equal capacitance, obtain the
relation between dielectric constants K, K1 and K2.
2. The given graph shows the variation of charge q versus potential difference V for capacitors C 1 and C1.
The two capacitors have same plate separation but the plate area of C2 is double than that of C1. Which of
the lines in the graph correspond to C1 and C2 and why?
3. A slab of material of dielectric constant K has the same area as that of the plates of a parallel plate
capacitor but has the thickness d/2, where d is the separation between the plates. Find out the expression
for its capacitance when the slab is inserted between the plates of the capacitor.
THREE Marks Questions
1. Network of four capacitors each of 12 F capacitance if connected to a 500 V supply as shown in the
figure. Determine What?
FIVE Marks Questions:
1.
An electric dipole moment p is held in a uniform electric field E.
(i) Prove that no translation force acts on the dipole.
(ii) Hence, prove that the torque acting on the dipole is given by pE sin, indicating the direction along
which it acts.
(iii) How much work is required in turning the electric dipole from the position of most stable equilibrium
to the position of most unstable equilibrium?
PHYSICS (Chapter–3)
CURRENT ELECTRICITY
TWO MARKS QUESTIONS:
1. Two cells E1 and E2 in the given circuit diagram have an emf of 5 V and 9 V and internal resistances of
0.3 and 1.2 , respectively. Calculate the value of current flowing through the r of 3.
2. A wire of 20 resistance is graduallystretched to double its original length. Then it is cut into two equal
parts. These parts are then connected in parallel across a 4.0 V battery. Find the current drawn from
thebattery.
THREE Marks Questions:
1. In the circuit shown, R1 = 4, R2 = R3 = 15, R4 = 30 and E = 10V. Calculate the equivalent resistance of
the circuit and the current in each resistor.
2. Calculate the equivalent resistance of the given electrical network between points A and B.
3. In a meter bridge, the null point is found at a distance of 60 cm from A. If a resistance of 5 is connected in
series with 5, the null point occurs at 50.0 cm from A. Determine the values of R and S.
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PHYSICS(Chapter-4)
MOVING CHARGES & MAGNETISM
TWO Marks Questions
1. Using Ampere’s circuital law, obtain an expression for the magnetic field along the axis of a current
carrying solenoid of length l and having N number of turns.
THREE Marks Questions:
1.
An electron moves around the nucleus in a hydrogen atom of radius 0.51 Å with a velocity of 2 × 105 m/s.
Calculate the following
(i) The equivalent current due to orbital motion of electron.
(ii) The magnetic field produced at the centre of the nucleus.
(iii) The magnetic moment associated with the electron.
FIVE Marks Questions:
1. (i) Draw a schematic sketch of a cyclotron.
Explain clearly the role of crossed electric and magnetic field in accelerating the charge. Hence derive the
expression for the kinetic energy acquired by the particles.
(ii) An -particle and a proton are released from the centre of the cyclotron and made to accelerate.
(a) Can both be accelerated at the same cyclotron frequency? Give reason to justify your answer.
(b) When they are accelerated in turn, which of the two will have higher velocity at the exit slit of the
does?
PHYSICS(Chapter-5)
MAGNETISM & MATTER
TWO Marks Questions:
1. The following figure shows the variations of intensity of magnetization (I) versus the applied
magnetic field intensity (H) for two magnetic materials, A and B.
(i) Identify the materials A and B.
(ii) For the material A, plot the graph between magnetic susceptibility and temperature.
2. Define magnetic susceptibility of a material. Name two elements, one having positive
susceptibility and the other having negative susceptibility. What does negative susceptibility
signify?
THREE Marks Questions:
1. (i) How does angle of dip change as line goes from magnetic pole to magnetic equator of the
earth?
(ii) A uniform magnetic field gets modified as shown below when two specimens X and Y are
placed in it. Identify whether specimens X and Y are diamagnetic, paramagnetic or ferromagnetic.
2. Deduce the expression for magnetic dipole moment of an electron revolving around the nucleus in
a circular orbit of radius r. Indicate the direction of the magnetic dipole moment.
PHYSICS(Chapter-6)
ELECTROMAGNETIC INDUCTION
TWO Marks Questions
1. Predict the polarity of the capacitor in the situation described by adjoining figure Explain the
reason too.
2. A coil, Q is connected to low voltage bulb B and placed near another coil, P as shown in the
figure. Give reasons to explain the following observations
(i) The bulb, B lights,
(ii) Bulb gets dimmer if the coil, Q is moved towards left.
THREE Marks Questions
1. A metallic square loop ABCD of size 15 cm and resistance 1.0 is moved at a uniform velocity of
v m/s, in a uniform magnetic field of 2 T, the field lines being normal to the plane of the paper.
The loop is connected to an electrical network of resistors, each of resistance 2. Calculate the
speed of the loop for which 2 mA current flows in the loop.
2. Define the coefficient of mutual induction. A long solenoid of length l and radius r1 is enclosed
coaxially within another long solenoid of length l and radius r2 (r2> r1 and l>> r2). Deduce the
expression for the mutual inductance of this pair of solenoids.
FIVE Marks Questions
1. State Faraday’s law of electromagnetic induction.
Figure shows a rectangular conductor PQRS in which the conductor, PQ is free to move in a
uniform magnetic field, B perpendicular to the plane of the paper.
The field extends from x = 0 to x = b and is zero for x> b.
Assume that only the arm, PQ possesses resistance, r.
When the arm, PQ is pulled outward from x =0 to x = 2b and is then moved backward to x = 0
with constant speed v, obtain the expressions for the flux’ and the induced emf.
Sketch the variation of these quantities with distance 0  x  2b .
PHYSICS(Chapter-7)
ALTERNATING CURRENT
TWO Marks Questions
1. Distinguish between the terms ‘average value’ and ‘rms value’ of an alternating current. The
instantaneous current from an AC source is, l = 5 sin 314 t A. What are the average and rms value
of the current?
THREE Marks Questions
1. In a series L-C-R circuit, define the quality factor, Q at resonance. Illustrate its significance by
giving one example. Show that power dissipated at resonance in L-C-R circuit is maximum.
2. The figure shows a series L-C-R circuit with L = 10.0 H, C = 40 F, R = 60 connected to a
variable frequency 240 V source, calculate
(i) the angular frequency of the source which drives the circuit at resonance.
(ii) the current at the resonating frequency.
(iii) the rms potential drop across the inductor at resonance.
FIVE Marks Questions
1. The given circuit diagram shows a series L-C-R circuit connected to a variable frequency 230 V
source
(i) Determine the source frequency which derives the circuit in resonance.
(ii) Obtain the impedance of the circuit and the amplitude of current at the resonating frequency.
(iii) Determine the rms potential drops across the three elements of the circuit.
(iv) How do you explain the observation that the algebraic sum of the voltages across the three
elements obtained in (c) is greater than the supplied voltage?
2. Derive an expression for the impedance of a series L-C-R circuit connected to an AC supply of
variable frequency.
Plot a graph showing variation of current with the frequency of the applied voltage. Explain
briefly how the phenomenon of resonance in the circuit can be used in the tuning mechanism of a
radio or a TV set?
PHYSICS(Chapter-8)
ELECTROMAGNETIC WAVES
TWO Marks Questions
1. An EM wave has amplitude of electric field E0 and amplitude of magnetic field is B0 the electric
3
field at some instant become E 0 . What will be magnetic field at this instant? (Wave is travelling
4
in vacuum).
2. Write Maxwell’s equations for electromagnetic waves.
THREE Marks Questions
1. Explain Davisson and Germer experiment to verify the wave nature of electrons.
2. What is Einstein’s explanation of photo electric effect? Explain the laws of photo electric
emissionon the basis of quantum nature of light.
PHYSICS(Chapter-9 & 10)
RAY OPTICS & WAVE OPTICS
TWO Marks Questions
1. Define critical angle for total internal reflection. Obtain an expression for refractive index of the
medium in terms of critical angle.
2.
Define diffraction. What should be the order of the size of the aperture to observe diffraction.
THREE Marks Questions
1. A plane wave front is incident on (i) a prism (ii) a convex lens (iii) a concave mirror. Draw the
emergent wave front in each case.
2. Obtain the formula for combined focal length of two thin lenses in contact, taking one divergent
and the other convergent.
FIVE Marks Questions
1. A light ray passes from air into a liquid as shown in figure. Find refractive index of liquid.
2. Draw a graph to show the angle of deviation with the angle of incidence i for a monochromatic
ray of light passing through a prism of refracting angle A. Deduce the relation

sin  A  m  / 2
sin A / 2
PHYSICS(Chapter-11)
DUAL NATURE OF RADIATION & MATTER
TWO Marks Questions
1. In a photoelectric effect experiment, the graph between the stopping potential V and frequency of
the incident radiation on two different metals P and Q are shown in Fig.
(i) Which of the two metals has greater value of work function?
(ii) Find maximum K.E. of electron emitted by light of frequency v = 8 × 1014 Hz for metal P.
2. Name the experiment for which the followings graph, showing the variation of intensity of
scattered electron with the angle of scattering, was obtained. Also name the important hypothesis
that was confirmed by this experiment.
THREE Marks Questions
1. (i) Draw a schematic diagram of the experimental arrangement used by Davisson and Germer to establish
the wave nature of electron.
(ii) Express the de-Broglie wavelength associated with electrons in terms of the accelerating voltage V.
(iii) An electron and a proton have the same kinetic energy. Which of the two will have larger wavelength
and why?
2. (i) Why photoelectric effect cannot be explained on the basis of wave nature of light? Give reasons.
(ii)Write the basic features of photon picture of electromagnetic radiation on which Einstein’s
photoelectric equation is based.
PHYSICS(Chapter-12 &13)
ATOM & NUCLIE
TWO Marks Questions
n1

0
1. A radioactive isotope decays in the following sequence A 
 A1 
 A 2 . If the mass and
atomic numbers of A2 are 171 and 76 respectively, find mass and atomic number of A and A1.
Which of the three elements are isobars?
2. Define the term half-life period and decay constant. Derive the relation between these terms.
THREE Marks Questions
1. State the law of radioactive decay. Plot a graph as a function of time (t) for a given radioactive species
having half life T1/2
Depict in the plot the number of undecayed nuclei at
(i) T = 2T1/2,
(ii) T = 5T1/2
2. The ground state energy of hydrogen atom is –13.6 eV. If an electron makes a transition from an energy
level –0.85 eV to –1.51 eV, calculate the wavelength of the spectral line emitted. To which series of
hydrogen spectrum does the wavelength belong?
FIVE Marks Questions
1. State Bohr’s postulates. Using these postulates, drive and expression for total energy of an electron
in the nth orbit of an atom. What does negative of this energy signify?
2. Define binding energy of nucleus. Draw a curve between mass number and average binding
energy per nucleon. On the basis of this curve, explain fusion and fission reactions.
PHYSICS(Chapter-14)
SEMICONDUCTOR ELECTRONICS
TWO Marks Questions
1.
Find the equivalent resistance of the network show in figure between point A and B when the p-n
junction diode is ideal and:
(i)A is at higher potential
(ii)B is at higher potential
2.
In the working of a transistor, emitter base junction is forward biased, while the collector base
junction is reverse based, why?
3.
The following figure shows the input waveform `A’ and `B’ and output wave form y of a gate.
Write its truth table and identify the gate.
THREE Marks Questions
1.
Draw V-I characteristics of a p-n junction diode. Answer the following questions, giving reasons.
(i) Why is the current under reverse bias almost independent of the applied potential up to a
critical voltage?
(ii) Why does the reverse current show a sudden increase at the critical voltage?
Name any semiconductor device which operates under the reverse bias in the breakdown region.
FIVE Marks Questions
2.
How does a transistor work as an oscillator? Explain its working with suitable circuit diagram.
Write the expression for frequency of output.
3. What are logic gates? Why are they so called? Draw the logic symbol and write truth table for
AND, OR and NOT gate.
PHYSICS(Chapter-15)
COMMUNICATION SYSTEM
TWO Marks Questions
1. Block diagram of a receiver is shown in the figure
THREE Marks Questions
2. The diagram given below represents the ‘block diagram’ of a generalized communication system.
Identify the elements, labeled as X, Y, Z in this diagram. Explain the function of each of these
elements.
3.
Draw a schematic diagram showing the
(i) ground wave (ii) sky wave and (iii) space wave propagation modes for em waves.
Write the frequency range for each of the following
(i) Standard AM broadcast
(ii) Television
(iii) Satellite communication