Sample Paper (CBSE) · 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

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


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?

1

1

1

1

1

2


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

2

2


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

2

2

3

3


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

3

3

3

3

3

3


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

3

3

3


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

3

3

3

4


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

5

5

5


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.

5

5

5


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


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


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.


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.


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,


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


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


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:


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.


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.


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.


b.


26.


Full wave rectifier works on the principle that a junction diode offers

low resistance during forward bias and high resistance when reverse

biased.

OR

Documents

Sample Paper (CBSE) · 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