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Sample Paper (CBSE)
Series PHY/SP/1E Code No. SP/1-E
SP/1-E ©Educomp Solutions Ltd. 2014-15
PHYSICS (Theory)
Time Allowed: 3 hours Maximum Marks: 70
General Instructions:
(i) All questions are compulsory.
(ii) This question paper has five sections: Section A, Section B, Section C, Section
D and Section E.
(iii) Section A contains five questions of one mark each, Section B contains five
questions of two marks each, Section C contains twelve questions of three
marks each, Section D contains one value based question of four marks and
Section E contains three questions of five marks each.
(iv) There is no overall choice. However, an internal choice has been provided in
one question of two marks, one question of three marks and all three questions
of five marks each weightage. You have to attempt only one of the choices in
such questions.
(v) You may use the following values of physical constants wherever necessary:
c = 3 × 108 m/s
h = 6.63 × 10-34 Js
e = 1.6 × 10-19 C
μo = 4 × 10-7
T mA-1
1
4 o = 9 × 109 N m2 C-2
me = 9.1 × 10-31 kg
Mass of Neutrons = 1.675 × 10-27 kg
Mass of proton = 1.673 × 10-27 kg
Avogadro’s number = 6.023 × 1023 per gram mole
Boltzmann constant = 1.38 × 10-23 JK-1
SP/1-E ©Educomp Solutions Ltd. 2014-15
Section A
1. What is the resistance offered by an inductance to d.c.?
2. Write the basic nuclear process of neutron undergoing β-decay.
3. Two identical loops, one of copper and another of aluminium are rotated
with the same speed in the same magnetic field. In which case the induced
current will be more and why?
4. What is the effect of change of wavelength of light on the speed of light in
vacuum?
5. What is the effect on the velocity of the photo-electrons, if the wavelength of
the incident light is decreased?
Section B
6. The ratio of the intensities at minima to the maxima in the Young's double
slit experiment is 9: 25. Find the ratio of the widths of the two slits.
7. Four point charges are placed at the four corners of a square in the two ways
as shown in figure (a) and (b). Will the 1) Electric field 2) electric potential
at the centre of the square be the same or different in the two configurations
and why?
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a.
b.
8. a. Why does the electric field inside a dielectric decrease, when it is placed
in an external electric field?
b. What is the angle between the directions of electric dipole moment and
electric field at any
1. Axial point and
2. Equatorial point due to an electric dipole?
9. The potential difference across a given copper wire is increased. What
happens to the drift velocity of the charge carriers? A potential difference V
is applied across a conductor of length L and diameter D. How are the
electric field E and the resistance R of conductor affected, when in turn
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SP/1-E ©Educomp Solutions Ltd. 2014-15
a. V is halved and
b. L is halved?
Justify your answer.
10. Figure shows an inductor L and a resistance R connected in parallel to a
battery through a switch. The resistance of R is the same as that of the coil
that makes L. Two identical bulbs are put in each arm of the circuit.
a. Which of the bulbs lights up earlier, when key K is closed? Why?
b. Will the bulbs be equally bright after some time? Give reason.
Section C
11. a. Which part of electromagnetic spectrum has the largest penetrating
power?
b. What is another name of infrared radiations? Why they are called so?
Name the radiations having shorter wavelength and longer wavelength
next to infrared radiations in an electromagnetic spectrum.
12. Calculate the half life period of a radioactive substance, if its activity drops
to 1/16 th of its initial value in 30 years.
OR
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SP/1-E ©Educomp Solutions Ltd. 2014-15
What fraction of tritium will remain undecayed after 50 years? Given, half
life of tritium is 12.5 years.
13. Draw the energy band diagram of an n-type semiconductor. How does the
forbidden energy gap of an intrinsic semiconductor vary with increase in
temperature?
14. State two factors by which the range of transmission of signals by a TV
tower can be increased.
15. a. Draw the plot of binding energy per nucleon (B.E./A) as a function of
mass number A. Write two important conclusions that can be drawn
regarding the nature of nuclear force.
b. Use this graph to explain the release of energy in both the processes of
nuclear fusion and fission.
16. Answer the followings:
a. Why is it necessary to introduce a cylindrical soft iron core inside the coil
of a galvanometer?
b. Increasing the current sensitivity of a galvanometer may not necessarily
increase its voltage sensitivity. Explain by giving reason.
17. A voltage is applied to a series LCR circuit. Derive the
expression for the average power dissipated over a cycle.
18. Three identical capacitors C1, C2 and C3 of capacitance 6 μF each are
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connected to a 12 V battery as shown in figure:
Find:
a. Charge on each capacitor
b. Equivalent capacitance of the network
c. The energy stored in the network.
19. a. A ray of light while travelling from a denser to rarer medium undergoes
total internal reflection. Derive the expression for the critical angle in
terms of the speed of light in the two media.
b. Calculate the speed of light in a medium whose critical angle is 45°.
20. a. Draw a ray diagram to show refraction of a ray of monochromatic light
passing through a glass prism.
b. How does the angle of minimum deviation of a glass prism vary if the
incident violet light is replaced by red light?
c. Out of blue and red light, which is deviated more by the prism? Why?
21. If the frequency of the incident radiation on the cathode of a photocell is
doubled, how will the following change:
a. Kinetic energy of the electrons
b. Photoelectric current
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c. Stopping potential
OR
What do you mean by the phrase “dual nature of radiation”? An electron and
alpha particle have the same kinetic energy. How are their de-Broglie
wavelengths associated with them related?
22. What is space wave propagation? If the sum of the heights of transmitting
and receiving antennae in line of sight of communication is fixed at h, show
that the range is maximum, when the two antennas have a height of h/2
each.
Section D
23. Priya was doing an experiment on comparison of e.m.f,’s using potentiometer
in Physics lab. She could not take the readings because the galvanometer
showed same side deflection. She checked the circuit and the connections
were correct. Her friend Sunita who was doing her experiment nearby came
to help her. Sunita increased the voltage of the eliminator by turning the
knob and supplying current to the potentiometer. Priya tried the experiment
again and got the readings. She thanked Sunita for her help.
a. What are the values displayed by both Priya and Sunita?
b. State one reason why the galvanometer showed same side deflection.
c. What is difference between e.m.f . and terminal potential difference?
Section E
24. a. Deduce an expression for the frequency of revolution of a charged particle
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in a magnetic field and show that it is independent of velocity or energy
of the particle.
b. 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.
OR
a. Define the terms magnetic inclination and horizontal component of
earth’s magnetic field at a place. Establish the relationship between the
two with the help of a diagram.
b. The vertical component of the earth’s magnetic field at a given place is
times its horizontal component. The total intensity of earth’s magnetic
field at the place is 0.5 G. Calculate the value of
1. angle of dip
2. the horizontal component of earth’s magnetic field.
25. a. Describe briefly how a diffraction pattern is obtained on a screen due to a
single narrow slit illuminated by a monochromatic source of light. Hence
obtain the conditions for the angular width of secondary maxima and
secondary minima.
b. Two wavelengths of sodium light of 590 nm and 596 nm are used in turn
to study the diffraction taking place at a single slit of aperture 2 × 10-6 m.
The distance between the slit and the screen is 1.5 m. Calculate the
separation between the positions of first maxima of the diffraction
pattern obtained in the two cases.
OR
a. What do you understand by polarization of a wave? Show by giving a
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suitable diagram, how unpolarized light can be polarized by reflection.
b. Two polaroids P1 and P2 are placed with their pass axes perpendicular to
each other. Unpolarised light of intensity Io is incident on P1. A third
Polaroid P3 is kept in between P1 and P2 such that its pass axis makes an
angle of 60º with that of P1. Determine the intensity of light transmitted
through P1, P2 and P3.
26. Draw forward and reverse characteristic curves of a pn-junction diode.
Explain briefly with the help of a circuit diagram, how a pn- junction diode
works as a full wave rectifier. Write down the principle on which full wave
rectifier works.
OR
Draw a labeled circuit diagram of a base-biased transistor in common-
emitter configuration operating as a switch. Plot the transfer characteristics
of this base-biased transistor indicating the different regions of its operation.
Explain briefly, how the transistor operates as a switch.
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1. For d.c., f = 0
Therefore, XL = 0
2.
3. The induced current will be more in copper loop as compared to the
aluminium because resistance of copper is less as compared to the
aluminium.
4. The speed of light in vacuum remains the same for all wavelengths.
5. The velocity of the photo-electrons increases, if the wavelength of the
incident light is decreased.
6. Given:
That is
7. i. Electric field will be different because electric field is a vector
quantity.
ANSWERS
SP/1-E ©Educomp Solutions Ltd. 2014-15
In case- a) there is a non-zero net electric field and in case b) net
electric field is zero.
ii. In both the cases the electric potential is zero because electric
potential is a scalar quantity.
8. a. Because the polarization of the dielectric opposes it.
b. 1. Zero
2. 180°
9. As the drift velocity of the electrons will also increase.
The resistance and electric field are given by:
a. There is no effect on resistance when V is halved. The electric field
will get halved when V is halved.
b. The resistance will get halved when Lis halved and electric field will
become twice.
10. a. The bulb B2 will light up earlier because the current through the
bulb B2 grows to maximum value instantaneously whereas the
current through bulb B1 will take some time to reach the maximum
value.
b. The bulb B1 will glow more brightly than B2 because the current
through bulb B2 will be less due to resistance R whereas after steady
state is reached self-inductance will have no effect.
11. a. Gamma rays
SP/1-E ©Educomp Solutions Ltd. 2014-15
b. Infrared radiations are also called as heat waves because they cause
the heating effect. Radiations having shorter wavelength and longer
wavelength next to infrared radiations in an electromagnetic
spectrum are visible light and microwaves.
12. Use the formula:
We get, T = 7.5 years.
OR
Use the formula:
We get,
13.
When the temperature of a semiconductor is increased, large number of
electron from valence band move to the conduction band. This may be
considered as if the forbidden energy gap has decreased.
14. a. By increasing the height of transmitting tower.
SP/1-E ©Educomp Solutions Ltd. 2014-15
b. By increasing the height of the receiving antenna.
15. a.
Conclusions:
1. The intermediate nuclei are more stable and have large value of
binding energy per nucleon.
2. Light and heavy nuclei are unstable nuclei having lower value of
binding energy per nucleon.
b. In nuclear fission reaction unstable heavy nuclei splits into two
stable intermediate nuclei and in nuclear fusion reaction two
unstable light nuclei combines to form stable intermediate nuclei. In
both processes energy liberates as stability increases.
16. a. By introducing a cylindrical soft iron core inside the coil of a
galvanometer, magnetic field is increased so sensitivity increases
and magnetic field becomes radial. So angle between plane of coil
and magnetic line of force is zero in all orientations of coil.
SP/1-E ©Educomp Solutions Ltd. 2014-15
b. For constant resistance, voltage sensitivity increases if current
sensitivity is increased. But if resistance of coil is also increases in
same ratio then voltage sensitivity may be constant.
17.
18. Given: C1 = C2 = C3 = 6 μF and V = 12 V
a. Charge on C3,
Charge on C1 and C2, .
b. Equivalent capacitance of the network,
c. The energy stored in the network,
19. a. We know,
b. Using the relation:
We get,
SP/1-E ©Educomp Solutions Ltd. 2014-15
20. a.
b. The angle of minimum deviation of a glass prism will decrease if the
incident violet light is replaced by red light because the refractive
index of glass for red light is less than that for the violet light.
c. We know that the deviation produced is given by:
Refractive index of glass for blue light is more than that of red light.
Thus the blue light will suffer more deviation than the red light.
21. The Einstein’s photoelectric equation is given by:
a. Kinetic energy of photoelectrons will increase if the frequency of the
incident radiation on the cathode of a photocell is doubled.
b. There is no effect of increase in frequency of the incident radiation
on the photoelectric current.
c. We know
SP/1-E ©Educomp Solutions Ltd. 2014-15
Thus the stopping potential will increase if the frequency of the
incident radiation on the cathode of a photocell is doubled.
OR
The phenomenon such as diffraction, interference and polarization can
be explained on the basis of wave nature of radiation whereas the
phenomenon such as Compton Effect and photoelectric effect can be
explained by particle nature of radiation. Thus the radiation has dual
nature.
From the de-Broglie equation:
We get,
22. When the radio waves from the transmitter reach the receiver either
directly or after reflection from ground or in troposphere, the wave
communication is called as space wave communication.
Using the relations
SP/1-E ©Educomp Solutions Ltd. 2014-15
We get,
23. a. Sharing of knowledge and helping others.
b. The emf of the driving cell should be greater than the emf of the
experimental cells.
c. E.m.f. is the potential difference between the terminals of a cell
when the cell is in the open circuit and terminal potential difference
is the potential difference between the terminals of a cell when the
cell is in the closed circuit.
24. a. For a particle performing circular motion, centripetal force is
provided by the magnetic force. That is:
SP/1-E ©Educomp Solutions Ltd. 2014-15
b.
Electric field gives the kinetic energy to the charged particle for
accelerating it and magnetic field provides the necessary centripetal
force for making it move in a circular path.
SP/1-E ©Educomp Solutions Ltd. 2014-15
OR
a. The angle made by the direction of the earth’s total magnetic field
with the horizontal direction is called as magnetic inclination or dip
(δ).
The component of earth’s magnetic field along the horizontal
direction is called as the horizontal component of earth’s magnetic
field (BH).
The relation between magnetic declination and horizontal component of
earth’s magnetic field is:
b.
SP/1-E ©Educomp Solutions Ltd. 2014-15
25. a.
Condition for minima
Condition of secondary maxima
b. Using the relation
The separation between the positions of first maxima of the diffraction
pattern obtained in the two cases is:
OR
a. The phenomenon due to which the vibrations of light are restricted
in a particular plane is called the polarization of light.
When light is incident at Brewster angle then the reflected light is
plane polarized.
SP/1-E ©Educomp Solutions Ltd. 2014-15
b.
SP/1-E ©Educomp Solutions Ltd. 2014-15
26.
SP/1-E ©Educomp Solutions Ltd. 2014-15
Full wave rectifier works on the principle that a junction diode offers
low resistance during forward bias and high resistance when reverse
biased.
OR
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