GURU HARKRISHAN PUBLIC SCHOOL
TILAK NAGAR
MOCK EXAMINATIONS 2014
PHYSICS-XII
Maximum Marks: 70
Time Allowed: 3Hrs
General Instructions:
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All questions are compulsory.
There are 29 questions in all.
Question number 1 to 8 carry 1 mark each.
Question number 9 to 16 carry 2 marks each.
Question number 17 to 26 carry 3 marks each.
Question numbers 27 to 29 are of 5 marks each.
Define electric dipole moment. Why two electric lines never cross each other?
An electric current is passed through a loop of flexible wire. What shape will it take?
How does self inductance of the coil will change when an iron rod is inserted in the coil?
A convex lens is held in water. What would be change in focal length?
Two radiations with frequency v and 2v are allowed to incident on a metal surface of work
function x, if both are greater than threshold frequency then in what condition the ejected
electron will have greater kinetic energy?
A.C. current gain in a CE transistor is 120. What is the change in collector current in the
transistor when the base current changes by 100µ A?
Draw a graph showing variation of potential energy of nucleons with inter nucleonic distance?
What is the percentage of light transmitted if the angle between polarizer and analyzer is
30*?
An induced emf has no direction of its own. Comment.
Derive an expression for the energy density of a capacitor.
If the atomic and mass numbers of nuclei are conserved during the nuclear reaction, then why
large amount of energy is is evolved in nuclear reactions.
A bulb and a capacitor are connected in series to an a.c. source of variable frequency. How
will the brightness of bulb change on increasing the frequency of a.c?
Draw a labeled diagram of Zener diode. Also draw a graph showing its characteristics.
How is the distance of closest approach change if the kinetic energy of alpha beam is
increased or if the nucleus f higher charge is used? Use relevant relation.
What is the principle of doorway metal detector installed at airports and metro stations?
State and prove Curie’s law in magnetism.
What is Critical angle? Derive an expression for it.
The refractive index of material of concave lens is n. it is immersed in a medium of refractive
index n1. A parallel beam of light is incident on the lens. Trace the path of the emergent ray if
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n>n1 and if n1>n.
A prism is made of glass of unknown refractive index. A parallel beam of light is incident on a
face of prism. By rotating the prism, the minimum angle of deviation is found to be 45*. What
is the refractive index of the prism? If the prism is now placed in water, what will be new
angle of minimum deviation? Given that refractive angle of prism is 60*.
Draw the energy distribution of energy pattern in interference and diffraction pattern. Give
two points of difference between interference and diffraction.
The frequency of radiation during reflection and refraction remains same. Why? Draw the
pattern of wave front for a beam of converging rays.
Derive an expression for the equation of resultant amplitude in a typical interference pattern.
Hence deduce the conditions for maxima and minima intensity for the interference pattern.
What is the advantage of using oil immersion objective in a typical microscope? Hence define
Resolving power and limit of resolution of microscope.
An equiconvex lens with radii of curvature of magnitude 10 cm each is put over a liquid layer
poured on the top of a plane mirror. A small needle with its tip on the principle axis of the
lens is moved along the axis until its inverted real image coincides with the needle itself. The
distance of the needle, from the lens is measured to be 15 cm. On removing the liquid layer
and repeating the experiment, the distance is measured to be 10 cm. Given that the two
values of distance measured represents focal length of the two cases, calculate the refractive
index of the liquid.
Draw an expression for the De Broglie wavelength of an electron. What if the electron is
accelerated through a potential difference of V volts and at a condition when the temperature
of system is T.
With the help of suitable diagram, derive an expression to prove that the charge will
necessarily flow from inner to outer surface of the cylinder whatever higher the potential is
present on outer cylinder.
Derive an expression for the magnetic field due to a circular coil carrying current on its axial
line. Hence draw a relevant variation of magnetic field with distance from the centre.
State the postulates of Bohr’s atomic theory. Use this to derive an expression for energy of
electrons in hydrogen atom.
With the help of a labeled diagram, describe the working of n-p-n common emitter transistor
as an amplifier. Hence prove that current gain in CE configuration is greater than that in CB
configuration.
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GURU HARKRISHAN PUBLIC SCHOOL
TILAK NAGAR
ANSWER KEY
PHYSICS XII
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The product of either charge and distance between them is called electric
dipole moment.
At the point of intersection, we can draw two tangents which means two
directions of electric fields at the same point which is not possible.
Acquire circular shape due to repulsion.
Increases according to relation XL = Lw
Increase in focal length according to lens maker formula
Radiation with frequency 2v emits photoelectrons with greater kinetic energy
according to photoelectric equation
Use β = ∆Ic/∆Ib
Potential energy is negative when the nucleons are far, it becomes minimum at
a point and then suddenly increases in positive. See NCERT
Use law of malus and then perform I-I’/I X 100
According to Lenz rule, the induced current flowing in the circuit always flow in
such a direction that it opposes the cause that produced it. So the increase or
decrease in magnetic flux decides the direction of induced current in the
circuit.
See NCERT
The difference in binding enthalpy of reactants and that in products always
results in energy during nuclear reaction.
As bulb represents a resistor. If frequency of a.c. is increased then according to
relation Xc = 1/cω, Xc decreases, hence current through circuit increases and
brightness of bulb increases.
See NCERT
According to relation, distance of closest approach is given by
D = 2ZKe2/rE
So D decreases if E increases and D increases if Z increases.
The doorway is actually a large inductive coil attached to a variable capacitor.
The system is set at Series Resonance in LCR so large amount of current is
passing through it. When we carry anything metallic, the circuit loses the
conditionof resonance and current falls in the circuit, which sounds an alarm.
Magnetic susceptibility of a paramagnetic substance is inversely proportional
to temperature in Kelvin.
For proof; see NCERT
The angle of incidence in denser medium for which the angle of refraction in
rarer medium is 90*.
Deduce for the expression µ= 1/ sinC
Converging path if n1>n and diverging path if n>n1 with diagrams
δ= 45, A= 60 then solve for µ using the relation
µ = sin(A+ δm)/sinA/2
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using µ’ = µ/n
solve again
20 See NCERT
21 Atoms of the materials are actually harmonic oscillators, which oscillate with a
natural frequency. When a light of given frequency falls on the surface of the
material, the atoms are thrown in forced oscillations due to which they radiate
energy in the same way as absorbed. Hence the frequency is not affected at all.
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See NCERT for diagrams
22 See NCERT
23 Using oil immersion objective, the magnifying power of the lens increases. The
minimum distance through which two nearly placed objects can be seen
separately is called limit of resolution. The inverse of resolution is called
magnifying power.
24 From the first measurement, we get the value of focal length f , the
combination of equiconvex lens and a plano concave lens. Hence F= 15 cm,
Focal length of equiconvex lens F1= 10 cm, then using the relation
1/f = 1/f1 + 1/f2,
Find the value of F2=-30cm
Then use lens maker formula for the equiconvex lens to obtain
µe = 1.5
then use plano convex lens and apply lens maker formula , we get
µ = 1.33
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See NCERT
See NCERT
See NCERT
See NCERT
See NCERT
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