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KENDRIYA VIDYALAYA DLW,VARANASI
SUBJECT: PHYSICS
CLASS XII
BLUE PRINT
S.NO
UNITS
VSA
(1
MARKS)
1.
ELECTROSTATICS
1(1)
2.
CURRENT
ELECTRICITY
MAGNETIC EFFECT
OF CURRENT&
MAGNETISM
ELECTROMAGNETIC
INDUCTION &
ALTERNATING
CURRENTS
ELECTROMAGNETIC
WAVES
OPTICS
--
3.
4.
5.
6.
7.
8.
9.
10
SA I
(2
MARKS)
SAII
(3
MARKS)
VB QUE.
(4
MARKS)
LA
(5
MARKS)
3(1)
4(1)
--
2(1)
--
--
5(1)
1(1)
4(2)
3(1)
--
--
1(1)
2(1)
--
--
--
3(1)
5(1)
--
--
--
5(1)
TOTAL
15
16
1(1)
2(1)
6(2)
DUAL NATURE OF
MATTER
ATOMS AND NUCLEI
1(1)
---
3(1)
--
--
6(2)
--
--
ELECTRONIC
DEVICES
COMMUNICATION
SYSTEM
--
--
6(2)
--
--
--
--
6(2)
--
--
12
TOTAL
5(5)
36(12)
4(1)
15(3)
70(26)
10(5)
17
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KENDRIYA VIDYALAYA DLW, VARANASI
I PRE-BOARD EXAMINATION 2014-15
CLASS XII
SUB: PHYSICS
TIME: 3 HRS.
MAX.MARKS.70
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
IX.
SET-II
All questions are compulsory.
There is no overall choice. However, an internal choice has been provided in one question of two marks,
one question of three marks & in all the three questions of five marks. You are to attempt only one of the
choices in such questions.
Question numbers 1-5 are very short answer type questions carrying one mark each.
Question numbers 6-10 are short answer type questions carrying two marks each.
Question numbers 11-22 are also short answer type questions carrying three marks each.
Question number 23 is value based question carrying 4 marks.
Question numbers 24-26 are long answer type questions carrying five marks each.
Use of calculator is not permitted; however, you may use log tables, if necessary.
You may use the following physical constants wherever necessary:
c=3 x 108 ms-1;
Boltzmann Constant `k’-1.38 x 1023 JK-1;
h=6.6 x10-34 Js;
e=1.6 x 10-19 C; Mass of neutron mn=1.6 x 10-27 Kg;
1. What orientation of electric dipole in a uniform electric field corresponds to its stable equilibrium?
2. The susceptibility of magnetic material is 1.9 x10-5. Name the type of material it represents.
3. Predict the direction of induced current in metal rings 1&2 lying in the same plane where the current I in
the wire is steadily increasing.
1
I
4.
5.
6.
7.
8.
9.
2
An alpha particle and a proton are accelerated from rest by the same potential .Find the ratio of their De
Broglie wavelengths.
A prism of angle 600 gives angle of minimum deviation of 300 .What is the refractive index of the material
of the prism?
State the principle of working of a transformer. Can a transformer be used to step up or step down dc
voltage. Why?
Two material Silicon & Copper are cooled from 300K to 60K.What will be the effect on resistivity? Give
reason for your answer.
An unpolarised light is incident on the boundary between two transparent media. State the condition
when reflected wave is totally plane polarized. Find out expression for the angle of incidence in this case.
An electron & proton enter a region of uniform magnetic field with uniform speed v in a perpendicular
direction as shown
p
x
x
x
x
x
B
e
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
(i) show the trajectories followed by the two particles
(ii) What is the ratio of radii of the circular paths.
10. A circular coil of closely wounded N turns & radius r carries a current I .Write the expression for the
following:
(i)The Magnetic field at the center.
(ii)Magnetic Moment of this coil.
OR
A short bar magnet of magnetic moment 0.9 J/ T is placed with its axis 300 to uniform magnetic field. It
Experiences a torque of 0.063 J.
(i)Calculate the magnitude of the magnetic field.
(ii)In which orientation will bar magnet be in the stable equilibrium in the Magnetic field.
11. An uniform electric field E=EX i N/C for x>0 and E= -EX i N/C for x<0 are given. A right circular cylinder of
length l cm and radius r cm has its centre at the origin and its axis along the X axis. Find out the net
outward flux. Using Gauss’s law, write the expression for the net charge within the cylinder.
12. (a)State the principle of working of moving coil galvanometer.
(b) “Increasing the current sensitivity of galvanometer may not necessarily increase its voltage
sensitivity.”Justify this statement.
13. Draw a ray diagram to show the image formation in a refracting type astronomical telescope in the near point
adjustment .Write down the expression for its magnifying power. Why should the diameter of the objective of
telescope be large?
14. Define the terms (i) cut off voltage (ii) threshold frequency in relation to the phenomena of photoelectric
effect. Using Einstein’s photoelectric equation show that the cut off voltage & threshold frequency for a
photosensitive material can be determined with the help of suitable plot/graph.
15. Draw the graph showing variation of Binding Energy per nucleon with the mass number .What are the main
inferences from the graph? How do you explain the constancy of Binding Energy in the range 30<A<170 using the
property that nuclear force is short ranged. Explain with the help of plot the release of energy in the processes of
nuclear fission & fusion.
16. Define half life period &decay constant of a radioactive sample. Derive the relation between the two terms.
OR
(a)Using Bohr’s second postulate of quantization of orbital angular momentum show that the circumference of
electron in the nthorbital state in Hydrogen atom is n times the De Broglie wavelength associated with it.
(b)The electron in Hydrogen atom is initially in the third excited state .What is the maximum number of spectral
lines which can be emitted when it finally moves to the ground state.
17. State the principle of working of p-n diode as rectifier. Explain with the help of circuit diagram, the use of p-n
diode as a full wave rectifier. Draw the sketch of input & output waveform.
18. Electromagnetic waves of wavelength
(i)λ 1 is used in satellite communication
(ii)λ2 is used to kill the germs in water purifier
(iii). λ 3 is used to detect leakage of oil in underground pipeline
(iv). λ 4 is use to improve visibility in runways during fog and mist conditions
a. Identify and name the part of electromagnetic spectrum to which these radiations belongs
b. Arrange this wavelength in ascending order of their magnitude
c. Write one more application of each .
19. Write two factors which justify the need for modulating signal. What is an amplitude modulated wave? Draw a
diagram showing Amplitude Modulated wave by superposing modulating signal over a sinusoidal carrier wave.
20. Mention the functions of
(i) transducer
(ii) repeater & (iii)transmitter
21. Draw the circuit diagram of Common Emitter amplifier using n-p-n transistor. Define voltage gain . Also draw
the input & output wave form of the transistor.
22. What is diffraction of light .Draw a graph showing variation of intensity with angle in single slit experiment.
Write one feature which distinguishes the observed pattern from the double slit interference pattern.
23. A man travelling in a car during thunderstorm sees a boy standing under a tree. He immediately stops his car
and asks the boy to get inside the car and saves him from possible natural calamity.
Answer the following question based on the above information.
1.
2.
3.
4.
What danger did the boy had while standing under the tree during the thunderstorm?
How is it safer inside the car during such weather?
What according to you are the values displayed by the man to help the boy?
Give another example from everyday life situations which represents display of similar values
24. What is induced emf? Write Faraday’s law of electromagnetic induction. Express it mathematically.
A conducting rod of length ‘l’ , with one end pivoted, is rotated with a uniform angular speed ‘w’ in a vertical
plane, normal to a uniform magnetic field B. Deduce an expression for emf induced in the rod. If resistance of rod
is R, what is the current induced in it.
OR
An ac source of voltage V= Vm sin wt is connected ,one by one,to three circuit elements X,Y &Z.It is observed that
the current flowing in them
(I) is in phase with applied voltage for element X.
(ii) lags the applied voltage, in phase, by angle π/2 for element Y.
(iii) leads the applied voltage, in phase, by π/2 for element Z.
Identify the three elements.
Find an expression for the current flowing in the circuit, when the same ac source is connected across a series
combination of the elements X, Y & Z.
If the frequency of the applied voltage is varied, set up the condition of the frequency when the current
amplitude in the circuit is maximum. Write expression for this current amplitude.
25 (a). State the principle of working of potentiometer
(b). Draw circuit diagram of potentiometer which can be used to determine internal resistance of the cell. Write
the formula used. How sensitivity can be increased?
(c) In a potentio meter arrangement a cell of e.m.f1.25 V gives balanced point at 35 cm length of Wire. If cell is
replaced by another cell the balance points shift 63 cm. What is the emf of second cell.
OR
Using the principle of Wheat stone Bridge describe the method to determine the specific resistance of wire in
laboratory .Draw the circuit diagram and write the formula used .Write any two precautions you would observe
while performing the experiment.
26. What is interference of light ? Write two essential conditions for sustained interference pattern to be
produced on the screen.
Draw a graph showing the variation of intensity v/s the position on the screen in Young’ s Experiment when.
a).Both the slits are opened and b).One of the slits is closed.
What is the effect on the interference pattern in Young’s double slit experiment when.
1. Screen is moved closer to the plane of the slits.
2. Separation between the two slits is increased .
Explain your answer in each Case.
OR
How is wave front defined? Distinguish between a plane wavefront and spherical wave front.
Using Huygen’s Construction, draw the figure showing the propagation of plane wavefront refracting at a plane
surface separating two media. Hence verify Snell’s law of refraction
When a light wave travels from rarer to denser medium, the speed decreases. Does it imply reduction of its
energy? Explain.
----------------------------------------------------------------------------------------------------------------------------
MARKING SCHEME
1.Dipole moment is along the electric field (1)
2.Paramagnetic (1)
3.
1
(1)
2
4.λα/λp=1/2√2 (1)
5. . µ=1.414
(1)
6.Principle(1)
No(1/2)
Justification(1/2)
7.Si-increases,Cu-decreases,reasons(1/2,1/2,1/2,1/2)
8.Condition – reflected ray should be perpendicular and refracted ray (1) Expression (1)
9.
x
x
x
x
p
X
x
x
x
e
X
x
x
x
X
x
x
x
r=mv/q B ,
re/rp=1/1840
10 (i)B=µONI/2r
(1)
(ii)m=NIA=NIπr2
(1)
(1)
(1)
Or
Torque=m B sin Φ (1)
When dipole moment is along the magnetic field,(1)
11.Calculation of net flux
Using φ=q/ε0
φ=Ex (2πr2 x 10-4)N m 2C-1
q= ε0 Ex (2πr2 x 10-4) C
12.Principle (1)
13Ray diagram (1)
(2)
(1)
No , Justification(0.5 ,1.5)
Expression(1)
To increase(i) intensity of image(ii)resolving power
14 .Definitions(1/2,1/2)
(any two reasons) (1/2,1/2)
Graph(1)
Determination of cut off voltage and threshold frequency from the plot explanation(1)
15.Graph(1)
Inferences(1)
Explanation of constancy of B.E./nucleon, nuclear fission& fission using the curve .(1/2,1/2,1/2)
16 Definition s of half life& decay constant (1/2,1/2) Derivation (2)
OR
(a)Expression for angular momentum (1.5)
(b)Derivation 2πrn=nλ
(1.5)
Possible transitions are ni=4 to nf=3,2,1 ni=3 to nf=2,1 ni=2 to nf=1 (no. of transitions=6) (1.5)
17 .Principle (1/2), Circuit diagram (1/2) Working (1) Input & output waveform(1/2,1/2)
18 (a)λ1- microwave, λ2 –UV, λ3-X ray , λ4-IR
(b) λ3< λ2< λ4< λ1
(1)
(1)
(c)any one application of each em wave(1)
19.(i)practical size of antenna(ii)to avoid mixing up of signals from different transmitter(iii)increase the power
radiated by antenna (any two )(1/2,1/2)
Definition(1/2)
Diagram(1.5)
20 (i)device which converts one form of energy to another (1)
(ii)combination of transmitter & receiver
(1)
(iii)transmits the signal (1)
21 Circuit diagram
(1)
Definition of voltage gain (1) Output & input waveform (1)
22.Bending of light around the corners
Intensity pattern diffraction at single slit
(1)
(1)
Difference between the interference and diffraction intensity pattern (1)
23.(i)Trees being taller than surrounding structures,may attract lightning and the boy may get electrocuted. (1)
(ii)car being a metallic body provides electrostatic screening.(1)
(iii)helpfulness,compassion,general awareness,services to others (1)
(iv)advising a person doing electrical repair without switching off the mains or
Stopping a person entering nuclear medicine ward without proper protection or any similar situation (1)
24 Definition (1/2) Faraday’s law of electromagnetic induction (1)
e=1/2 Bwl2(2) I=Bwl2/2R(1)
,mathematical expression(1/2)
OR
X-resistor,Y-inductor,Z-Capacitor(1/2,1/2,1/2)
Expression for current amplitude in series LCR
Condition for max. current(1)
Expression for the current amplitude(1/2)
(2)
Deducing
25.(a)Principle (1/2)
(b),Circuit diagram(1)
Formula used(1) ,
potential gradient should be reduced(1/2)
(c)Calculation and determination of E=2.25V (2)
OR
Principle(1/2) Circuit diagram(1)
Method(2),
Formula used(1/2) Two precautions(1/2,1/2)
26.Meaning of interference of light(1/2),
Two conditions(1/2,1/2)
(a)Intensity vs position curve of Interference of light(1)
(b) Intensity vs position curve of diffraction of light(1)
(i) fringe width decreases (1/2) (ii) fringe width decreases (1/2)
OR
Wavefront-locus of all particles of medium vibrating in the same phase (1/2)
Difference (1)
Figure(1)
Verification of Snell’s law(1.5)
No (1/2), energy of wave depends on its frequency and not on its speed.(1/2)