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Sample Paper (CBSE)
Series PHY/SP/1B Code No. SP/1-B
SP/1-B ©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-B ©Educomp Solutions Ltd. 2014-15
Section A
1. How can a galvanometer be converted into voltmeter?
2. What happens to then drift velocity of electrons, if length of a
conductor is doubled keeping the potential difference constant?
3. The electric field part of an electromagnetic wave in a medium
is represented by
Calculate the wavelength of the wave.
4. What is the rest mass of photon?
5. Which type of biasing gives a semiconductor diode very high
resistance?
Section B
6. Draw a plot of the binding energy per nucleon as a function of
mass number for large number of nuclei, 2 ≤A≤240. How do
you explain the constancy of binding energy per nucleon in the
range 30 ≤A≤170 using the property that nuclear force is short
ranged?
7. Give the direction in which the induced current flows in the
coil mounted on an insulating stand, when a bar magnet is
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SP/1-B ©Educomp Solutions Ltd. 2014-15
quickly moved along the axis of the coil from one side to the
other as shown in the figure.
8. Draw the graph showing the variation of reactance of a
capacitor and an inductor with the frequency of an a.c. circuit.
9. An object is kept in front of a concave mirror of focal length 15
cm. The image formed is three times the size of the object. Find
two possible distances of the object from the mirror.
OR
What is the polarizing angle of a medium of refractive index
.
10. In a meter bridge, the balance point is found to be at 39.5 cm
from the end A, when the resistor Y is of 12.5 ohm as shown in
figure. Determine the resistance of X. What happens if the
galvanometer and cell are interchanged at the balance point of
the bridge?
2
2
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SP/1-B ©Educomp Solutions Ltd. 2014-15
Section C
11. a. Explain, whether an induced current will be developed in a
conductor, if it is moved in a direction parallel to magnetic
field.
b. An electron in an atom revolves around the nucleus in an
orbit of radius 0.53 Å. Calculate the equivalent magnetic
moment, if the frequency of revolution of electron is 6.8 ×
109 MHz.
12. a. Two charges of magnitudes + 4Q and –Q are located at
points (a, 0) and (–3a, 0) respectively. What is the electric
flux due to these charges through a sphere of radius '2a'
with its centre at the origin?
b. Two point electric charges of unknown magnitude and sign
are placed at a distance apart. The electric field intensity is
zero at a point not between the charges but on the line
joining them. Write two essential conditions for this to
happen.
13. a. How is the focal length of a spherical mirror affected when
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SP/1-B ©Educomp Solutions Ltd. 2014-15
the wavelength of the light used is increased?
b. If ε0 and μ0 are the electric permittivity and magnetic
permeability in free space, ε and μ are the corresponding
quantities in a medium, then calculate the index of
refraction of the medium.
14. a. Define input resistance of a transistor used in its common
emitter configuration.
b. Draw the truth table of the following combination of gates:
15. By what percentage will the transmission range of a TV tower
be affected, when the height of the tower is increased by 21 %?
16. Two cells of e.m.f. 1.5 V and 2 V and internal resistances 1 Ω
and 2 Ω respectively are connected in parallel so as to send
current in the same direction through an external resistance of
5 Ω. Draw the circuit diagram. Using Kirchhoff’s laws,
calculate the current through each branch of the circuit and
potential across the 5 Ω resistance.
17. Derive an expression for the average power consumed in a
series LCR circuit connected to a.c. source in which the phase
difference between voltage and current in the circuit is φ.
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SP/1-B ©Educomp Solutions Ltd. 2014-15
Define the quality factor in an a.c. circuit.
18. A convex lens made up of glass of refractive index 1.5 is
dipped, in turn, in
a. medium A of refractive index 1.65
b. medium B of refractive index 1.33.
Explain giving reason whether it will behave as a converging
lens or a diverging lens in each of these two media.
OR
What is the effect on the interference fringes in a Young’s
double slit experiment due to each of the following operations:
a. The screen is moved away from the plane of the slits
b. The separation between the two slits is decreased
c. The monochromatic source is replaced by a source of white
light.
19. Define resolving power of a compound microscope. How does it
change on:
a. decreasing the wavelength of light used and
b. decreasing the diameter of its object lens?
20. Figure shows the variation of stopping potential V0 with the
frequency of incident radiation for two photosensitive metals A
and B.
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SP/1-B ©Educomp Solutions Ltd. 2014-15
a. Which of the metals has larger threshold wavelength?
Give reason.
b. Which metal gives out electrons having larger kinetic
energy for the same wavelength of incident radiation?
Explain why?
c. If the distance between the light source and metal A is
halved, how will the kinetic energy of electrons emitted
change? Why?
21. Explain briefly, with the help of circuit diagram, how a p-n
junction diode work as half wave rectifier?
22. Draw a simple demodulation circuit and explain its working.
Section D
23. Muthuswami a resident of Kundakulam was all set to leave
everything and shift to another place in view of the decision of
Govt. to start nuclear thermal power plant at Kundakulam.
His granddaughter Prachi, a science student was really upset
on the ignorant decision of her grandfather. She could finally
convince him not to shift, since adequate safety measures to
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SP/1-B ©Educomp Solutions Ltd. 2014-15
avoid any nuclear mishap have already been taken by the
Govt. before starting nuclear thermal plants.
a. What is the value displayed by Prachi in convincing her
grandfather?
b. What is the principle behind working of nuclear reactor?
c. Why is heavy water used as moderator?
Section E
24. a. A parallel plate capacitor of capacitance C is charged to a
potential difference V and then the battery is disconnected.
Now a dielectric slab of the dimensions equal to the spacing
between the plates is inserted between the plates. What are
the changes, in the capacitance, charges, potential
difference, electric field and the energy stored?
b. A parallel plate capacitor of capacitance C is charged to a
potential V. It is then connected to another uncharged
capacitor having the same capacitance. Find out the ratio of
the energy stored in the combined system to that stored
initially in the single capacitor.
OR
a. Derive an expression for the maximum torque acting on an
electric dipole, when held in a uniform electric field.
b. Consider two hollow concentric spheres, S1 and S2, enclosing
charges 2Q and 4Q respectively as shown in the figure.
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SP/1-B ©Educomp Solutions Ltd. 2014-15
1. Find out the ratio of the electric flux through them.
2. How will the electric flux through the sphere S1 change if
a medium of dielectric constant 'εr' is introduced in the
space inside S1 in place of air? Deduce the necessary
expression.
25. State Biot-Savart law and give the mathematical expression
for it. Use this law to derive the expression for the magnetic
field due to a circular coil carrying current at a point along its
axis. How does a circular loop carrying current behave as a
magnet?
OR
a. Draw a labelled diagram of a moving coil galvanometer.
Describe briefly its principle and working.
b. Answer the following :
1. Why is it necessary to introduce a cylindrical soft iron
core inside the coil of a galvanometer?
2. Increasing the current sensitivity of a galvanometer may
not necessarily increase its voltage sensitivity. Explain,
giving reason.
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SP/1-B ©Educomp Solutions Ltd. 2014-15
26. a. With the help of ray diagram, explain the phenomenon of
total internal reflection.
b. Obtain lens makers formula using the expression
Here the ray of light propagating from a rarer medium of
refractive index to a denser medium of refractive index
is incident on the convex side of spherical refracting surface
of radius of curvature R.
OR
a. Deduce the expression for the refractive index of glass in
terms of angle of prism and angle of minimum deviation.
b. Out of blue and red light, which is deviated more by a
prism? Give reason.
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SP/1-B ©Educomp Solutions Ltd. 2014-15
1. By connecting a suitable high resistance in series to the coil of a
galvanometer.
2. The drift velocity will become half of the initial value and resistance
will become double.
3. 200 m
4. Zero
5. Reverse biasing
6.
The constancy of binding energy per nucleon in the range 30 ≤A≤170
shows that a nucleon in the nucleus is not attracted by all the
remaining nucleons. It is attracted only by its some close neighbours
and hence the nuclear force is short ranged.
ANSWERS
SP/1-B ©Educomp Solutions Ltd. 2014-15
7. a. When magnet moves towards the coil, the current flows in clockwise
direction and
b. When magnet moves away from the coil, the current flows in anti-
clockwise direction.
8.
9. a. Use the relations:
b. For real image object distance is – 20 cm and for virtual image object
distance is – 10 cm.
OR
Use the relation
We get i = 60°
SP/1-B ©Educomp Solutions Ltd. 2014-15
10. Use the relation:
We get, X = 8.16 ohm
If the galvanometer and cell are interchanged at the balance point of
the bridge, the galvanometer will not show any deflection as the
condition for a balanced bridge is still satisfied.
11. a. Since Lorentz force on the free electrons in the conductor is zero, no
potential difference is produced across the ends of the conductor and
hence no induced current will be developed.
b. Using the relations:
We get, M = 9.6 × 10-24 Am2
12. a.
b. Both the charges are of opposite sign or nature.
The point where electric field intensity is zero is closer to the
smaller charge.
13. a. No change in the focal length of a spherical mirror on increasing the
wavelength of light used.
b. The index of refraction of the medium is
SP/1-B ©Educomp Solutions Ltd. 2014-15
14. a. The input resistance of a transistor used in its common emitter
configuration is defined as the ratio of small change in base-emitter
voltage to the small change produced in base current at constant
collector-emitter voltage.
b.
A B y’ y’’ Y
0 0 1 1 0
1 0 0 1 1
0 1 1 0 1
1 1 0 0 1
15. Use the formula:
The percentage increase in the transmission range of the TV tower is
10 %.
16.
a. I1 = 0.0294, I2 = 0.2647 and
b. Potential difference across R = 1.4705 V
SP/1-B ©Educomp Solutions Ltd. 2014-15
17. a. The average power consumed in a series LCR circuit connected to
a.c. source in which the phase difference between voltage and
current in the circuit is φ is given by
b. The quality factor of a resonant LCR-circuit is defined as the ratio of
the voltage drop across inductor to the applied voltage.
18. Use the formula:
a. In medium A lens will behave as a diverging lens.
b. In medium B lens will behave as a converging lens.
OR
a. Fringe width will increase as D increases.
b. Fringe width will increase as d decreases.
c. The colours of white light will produce interference pattern. The
central bright fringe is white in colour and the fringes closest on
either side of it is blue and farthest is red.
19. Resolving power of a microscope is defined as the reciprocal of the least
separation between two close objects so that they appear just separated
when seen through the microscope.
a. Resolving power of a microscope will increase on decreasing the
wavelength of light.
SP/1-B ©Educomp Solutions Ltd. 2014-15
b. Resolving power of a microscope will decrease on decreasing the
diameter of its object lens.
20. a. The metal A has larger threshold wavelength as it has smaller
threshold frequency.
b. The metal A gives out electrons having larger kinetic energy for the
same wavelength of incident radiation because it has smaller
threshold frequency and hence smaller work function.
c. If the distance between the light source and metal A is halved, the
kinetic energy of electrons emitted will remain unchanged because
the change in intensity of the incident radiation does not affect the
kinetic energy of the emitted electrons.
21.
SP/1-B ©Educomp Solutions Ltd. 2014-15
When an alternating voltage is applied across a diode in series
with a load resistance, a pulsating output voltage appears across
the load only during the half cycles of the a.c. when the diode is
under forward bias. The corresponding circuit is called a half-
wave rectifier circuit as shown in the image.
When the secondary of the transformer supplies a.c. voltage
across the terminals A and B, then in the positive half-cycle of
a.c. there is a current through the load RL when the diode is
under forward bias.
In the negative half-cycle of a.c. there is no current through the
load RL when the diode is under reverse bias.
The output voltage is in the form of varying pulses restricted to
only one direction.
22.
Working of Demodulation Circuit: The current flows through the
diode only during the positive half cycle of the AM wave. The
envelope of the rectified wave is the information signal (fm). The
SP/1-B ©Educomp Solutions Ltd. 2014-15
signal fm is separated from the carrier wave using the RC filter and
given to an amplifier. The output voltage of amplifier is connected to
a loud speaker which produces the original sound waves.
23. a. Awareness, social responsibility
b. Controlled fission chain reaction
c. Ordinary water absorb neutron at a fast rate. To overcome this
difficulty, Heavy water is used as a moderator which has negligible
cross sections for neutron absorption.
24. a. The capacitance increases, charge remains the same, potential
difference decreases, electric field decreases and energy stored in the
capacitor also decreases.
b. Using the formula:
We get, the ratio of the energy stored in the combined system to that
stored initially in the single capacitor as 1:2.
SP/1-B ©Educomp Solutions Ltd. 2014-15
OR
a.
b. 1. Using Gauss theorem,
2. If S1 is filled with medium of dielectric constant 'εr', then
25. Biot Savart law states that the magnetic field produced due to a small
conductor of length dl carrying a current I at a point at distance r
is given by
SP/1-B ©Educomp Solutions Ltd. 2014-15
Where k is the constant of proportionality and θ is the angle
between the current and the line joining the small conductor to the
observation point.
The magnetic field due to a circular coil carrying current at a point
along its axis is given by,
Where a is the radius of the circular coil, x is the distance from the
centre of the coil, n is the number of turns in the coil and I is the
current flowing in the coil.
The magnetic field pattern produced by a circular loop is similar to
that of a magnet.
OR
a.
Principle: When a current carrying coil is placed in magnetic field, it
experiences a torque.
SP/1-B ©Educomp Solutions Ltd. 2014-15
b. 1. It is necessary to introduce a cylindrical soft iron core inside the
coil of a galvanometer to increase the sensitivity and hence magnetic
field becomes radial.
2. We know that
If the resistance of the coil is constant then voltage sensitivity is
proportional to current sensitivity. But if resistance of the coil also
increases then in that case on increasing the current sensitivity the
voltage sensitivity remains constant.
26.
a.
b.
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