Physics

Class XII

BLUE PRINT

Key: Total marks (no. of questions).

*Value Based Question

Note:

— Value Based Questions may be asked from any unit/chapter/topic.

— It will consist of 3–5 marks.

SAMPLE PAPER

KENDRIYA VIDYALAYA SANGATHAN JMMU REGION

CLASS XII PHYSICS

Time allowed : 3 hours Maximum marks : 70

General instructions:

(a) All questions are compulsory.

(b) There are 30 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry

two marks each, questions 19 to 27 carry three marks each and questions 28 to 30 carry five

marks each. ,

(c) 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. You have to attempt only one of the given

choices in such questions.

(d) Use of calculators is not permitted.

(e) You may use the following values of physical constants wherever necessary:

C= 3x10 - 1ms - 1 . h = 6.626 x lQ-34Js

e = 1.602xlO -19C un=4πxlO - 7TmA - 1 . : Boltzmann’s constant k - 1.381 x 1Q-23 J K-1

Avogadro's number NA = 6,022 x 1023/mo!e

Mass of neutron mn = 1.0 X 1-'27 kg

Mass of electron me = 9.1 x 10~31 kg

Radius of earth = 6400 km

1. Two dipoles made from charge ± q and ± Q respectively have equal dipole moments. Find the ratio between the separation

between these two pairs of charge.

2. Why are alloys are used for making standard resistance coils?

3. Is Ohm’s Law is true for all conductors? Name two types of commercially available resistors.

4. How does the focal length of a lens change when Red light is replaced by Blue light?

5. Figure (i) shows rectangular loop shape moving into a region of a magnetic field which is directed normal to the

plane of the loop away from the reader. Determine the direction of induced current in this loop using Lenz’s law.

Fig (i) Fig (ii)

6. If the magnetic field is parallel to the positive y-axis and the charged particle is moving along the positive x-axis as

shown

in fig (ii) which way would the Lorentz force be for a proton (positive charge).

7. Give one example each of a ‘system’ that uses the (i) Sky wave (ii) Space wave mode of propagation.

8. Why is the ground wave transmission of signal s restricted to a frequency of 1500 Khz?

9. Keeping the voltage of the the charging source constant, what would be the percentage change in the energy stored

in a parallel plate capacitor if the separation between its plates were to be decreased by 10%?

10. Derive an expression for drift velocity of free electrons in a conductor in terms of relaxation time.

11. Kamla peddles a stationary bicycle the pedals of the bicycle are attached to a 100 turn coil of area 0.10 m2.

The coil rotates at half a revolution per second and it is placed in a uniform magnetic field of 0.01 T

perpendicular to the axis of rotation of the coil. What is the maximum voltage generated in the coil?

12. Find the ratio of intensities of two points P and Q on a screen in Young,s double slit experiment when waves from source S1 and

S2 have phase difference of (i) 00 and (ii)

13. A monochromatic source, emitting light of wavelength, 600 nm, has a power output of 66W. Calculate the number of

photons emitted by this source in 2 minutes.

14 N spherical droplets, each of radius r, have been charged to have a potential V each. If all these droplets were to

coalesce to form a single large drop, what would be the potential of this large drop? (It is given that the capacitance of a

sphere of radius kx.)

OR

Two point charges, q1 and q2, are located at points (a, o, o) and (o, b, o) respectively. Find the electric field, due to both

these charges, at the point, (o, o, c).

15.With the help of an example, explain how the neutron to the proton ratio change during decay of a nucleus.

16. Give two differences between a photo diode and a LED. Also, sketch a I – V characteristics of a

photodiode for different intensities

17. State Gauss's theorem in electrostatics. Apply this theorem to derive an expression for electric field intensity at a

point near an infinitely long straight charged wire.

18. The galvanometer, in each of the two given circuits, does not show any deflection. Find the ratio

of the resistors R1 and R2, used in these two circuits.

19. with the help of a labelled diagram, the principle of a cyclotron. Deduce an expression for the cyclotron frequency

and show that it does not depend on the speed of the charged particle.

Or

Distinguish the magnetic properties of dia, para- and ferro-magnetic substances in terms of (i) susceptibility, (ii)

magnetic permeability and (iii) coercivity. Give one example of each of these materials.

.

20. : (a) Does every charge give out electromagnetic waves? Explain very briefly. (1)

(b) The magnetic field in a plane EM wave is given by

By = 2 × 10 -7

sin (0.5 × 103 z + 1.5 × 10

11 t) T.

(i) What is the frequency of the wave?

(ii) Write an expression for the electric field. '

.

21. Define the term ‘wavefront’. Draw the wavefront and corresponding rays in the case of a

(i) diverging spherical wave, (ii) plane wave.

22. Three identical polaroid sheets P1, P2, and P3 are oriented so that the (pass) axis of P2 and P3 are inclined at

angles of 60° and 90°, respectively, with respect to the (pass) axis of P1. A monochromatic source, S, of intensity I0, is

kept in front of the polaroid sheet P1. Find the intensity of this light, as observed by observers O1, O2, and O3,

positioned as shown below.

23. Obtain the maximum kinetic energy of -particles, and the radiation frequencies of decays in the decay scheme

shown in Fig. . You are given that

m(198Au) = 197.968233 u

m(198Hg) =197.966760 u.

Draw a schematic arrangement of the Geiger - Marsden experiment. How did the scattering of a-particles by a thin foil

of gold provide an important way to determine an upper limit on the size of the nucleus ? Explain briefly.

24. What is binding energy? Using the curve of binding energy per nucleon as a function of mass number A. state clearly

how the release in energy in the process of nuclear fission and fusion can be explained.

25. Block diagram of a receiver is shown. Identify X, Y and Z. State their functions.

26. Suhasini’s uncle, was advised by his doctor to have an MRI scan of his chest. Her uncle did not know much

about the details and significance of this test. He also felt that it was too expensive and thought of postponing it.

When Suhasini learnt about her uncle’s problems, she immediately decided to do something about it. She took

the help of her family, friends and neighbours and arranged for the cost of the test. She also told her uncle that

an MRI (Magnetic Resonance Imaging) scan of his chest would enable the doctors to know of the condition of his

heart and lungs without causing any (test related) harm to him. This test was expensive because of its set up that

needed

strong magnetic fields (0.5 T to 3T) and pulses of radio wave energy. Her uncle was convinced and had the

required MRI scan of his chest done. The resulting information greatly helped his doctors to treat him well.

(a) What according to you, are the values displayed by Suhasini and her (2) family, friends and neighbours to

help her uncle? 2

(b) Assuming that the MRI scan of her uncle’s chest was done by using a magnetic field of 1.0 T, find the

maximum and minimum values of force that this magnetic field could exert on a proton (charge = 1.6 × 10–19)

that was moving with a speed of 104 m/s. State the condition under which the force has its minimum val

27.

28. (i) Derive the mirror formula which gives the relation between f, v and u. What is the corresponding formula for a

thin lens?

(ii) Calculate the distance d, so that a real image of an object at O, 15cm in front of a convex lens of focal length 10cm

be formed at the same point O. The radius of curvature of the mirror is 20cm. Will the image be inverted or eract?

OR

(i) Using the relation for refraction at a single spherical refracting surface, derive the lens maker’s formula.

(ii) In the accompanying diagram, the direct image formed by the lens (f = 10cm) of an object placed of O and that

formed after reflection from the spherical mirror are formed at the same point . What is the radius of curvature of the

mirror?

29.

Or

MARKING SCHEME

Q. no.

Answer Marks

1. As q a = Q a’

=

1

2. Because they have low value of temp coefficient of resistance and high resistivity

1

3. No, it is true for metallic conductors. Commercially available resistors are Carbon resistor and Wire bound resistors.

(½+ ½)

4.

= (µ - 1)(

) as µb > µr therefore

fb < fr i.e focal length of a lens decreases

1

5.

The magnetic flux through the rectangular loop abcd increases, due to the motion of the loop into the

region of magnetic field, The induced current must flow along the path bcdab so that it opposes the

increasing flux. 1

6.

The velocity v of particle is along the x-axis, while B, the magnetic field is along the y-axis, so v × B is

along the z-axis (screw rule or right-hand thumb rule). So, for a positive charge (proton) the force is

along +z axis. 1

7.

(i) Short wave broadcast services ½

(ii) Television broadcast (or microwave links or Satellite communication) (½+ ½)

8. In ground wave propagation , the loss of energy due to intraction with matter increases with increase with the frequency of wave . therefore, the wave of frequency 1500 hz is restricted

1

9.

1

½

½

10. derivation 2

11.

Here f = 0.5 Hz; N =100, A = 0.1 m2 and B = 0.01 T. Employing

= NBA 2 v

= 100 × 0.01 × 0.1 × 2 × 3.14 × 0.5

= 0.314 V

The maximum voltage is 0.314 V.

We urge you to explore such alternative possibilities for power generation.

½

1½

12. In young,s double slit experiment , the resultant intensity at any point on the screen is

I = I1 + I2 + 2√

Here I1 + I2 = I0

(i) 4 I0 (ii) 2 I0

Ratio is 2:1

½

½

½

½

13. ½

½

½

½

14.

½

½

½

½

½

½

½

½

15. Consider the decay of nucleus

Before decay neutron to proton ratio, n/p

After decay neutron to proton ratio, n/p

We find that ratio increases

½

½

1

16. Difference, I –V charestristics curve 1,1

17. Statement, Explanation 1,2

18.

For circuit 1, we have, (from the Wheatstone bridge balance condition),

R1 6

In circuit 2, the interchange of the positions of the battery and the galvanometer, does not change

the (Wheatstone Bridge) balance condition.

or R2 4½

½

½

½

½

1

19. Diagram,principal,expression

Difference for each

1,1,1

1,1,1

20.

(a) no , explanation

(b) (i) 23.9 GHz

1 1 1

(ii) Ez = 60 sin (0.5 × 103x + 1.5 × 1011 t) V/m

21. Definition,diagram 1,2

22.

1

1

1

23.

3

24. Definition, explanation 1,2

25. X= I F satage

Y= detector

Z = detector

1

1

1

26.

(a) (i) Presence of mind

High degree of general awareness

Ability to take prompt decisions

Concern for her uncle (Any two)

(ii) Empathy: Helping and caring nature (b) Maximum force = qvB ½

1.61019 104 1N

1.61015 N ½

Minimum force = zero ½

Condition: when v

is parallel to B

½ + ½

½ + ½

½

½

27.

28.

(i) Derivation of formula

Then lens formula

(ii)Numerical

Distance of this image from the mirror must be 20 cm ½

[ For image to from at O,

mirror must reverse the light d = (30 + 20) cm = 50 cm) ½

The final image is inverted.

OR

Statement of formula for single surface

(i) Derivation :

(ii) Numerical

2½

½

½ ½ 1

½ 2½ 1 1

29.

or

½

½

2

2

2

2

1

VALUE BASE QUESTIONS ON COMMUNICATION SYSTEM

1. Deepa’s uncle wants to talk to his son in USA. He does not have much money to spend on telephone calls. He has a

computer at his home. Deepa told her uncle that he can talk to his son with the help of computer and told him about

internet. Her uncle now talks to his son every day. He thanked Deepa for giving useful advice.

• What according to you are the values displayed by Deepa.

• How does internetwork?

2. Group discussion was arranged in class XII on the topic atmosphere. Three groups were made. Teacher asked the

Question. “Why can moon be not used as a communication satellite?” Answers were given by all the three groups.

Each group can give only one reason. Teacher told them that reason given by each group is correct. The groups

collected all the three reasons and come to correct conclusion.

(i) What values were showed by all the three groups?

(ii) Give the correct reason for the above question.

3. Chitra was watching her favorite TV serial suddenly the picture started shaking on TV screen. She asked her brother

to check the dish antenna. Her brother found no problem in dish. Chitranoticed the same problem in TV picture

again after some time. At the same time she heard the sound of low flying air craft passing over their house. She

asked her brother again. He explained the cause of shaking picture on TV screen when air craft passes over head.

• Name the values used by Chitra’s brother ?

• Why the picture on the TV screen was shaking when air craft was passing over head?

4. In the famous conversation, Rakesh Sharma, the first Indian astronaut in space, was asked by the then prime

minister Indria Gandhi as to how India looked from space. To which He replied ‘Sare Jahan Se Achcha’ (better then

the whole world.)

Answer the following questions based on the above passage:

(i) Which scientific mode of communication enabled The Prime Minister to speak to the Astronaut?

(ii) Name the scientific values displayed in this anecdote.

(iii) Which values are being reflected in the replygiven by the astronaut?

(iv) Give one more example of this scientific mode of communication in everyday life situations.

5. Advancements in communication principles and technology has helped mankind to communicate almost instantly in any part of

the globe. These advancements, however, have also

shown adverse effects. Many school authorities and parents are not in favour of free and

unlimited access of these electronic devices to students fearing adverse effect on their emotional

and psychological health.

Answer the following questions related to the information in the above passage:

(i) Name any three electronic devices which are used for instant communication.

(ii) Write any two adverse effects of misuse of these devises on students.

(iii) Which two values are adversely affected due to misuse of these communication devices.

(iv) (iv) Given one suggestion to promote/inculcate these values in school-going student.

1. • Brotherhood, team spirit, critical thinking

• NCERT chapter on Principles of Communications

2. • Team work, Awareness. • In the detection of forged documents, finger prints.

3. (i) Critical thinking and problem solving

(ii)Low lying air crafts reflect TV signals. Due to interference between direct signal received by

antenna and reflected signal the picture on TV shakes

4. (i) Radiowave communication system.

(ii) Use of scientific and technological advancement in service to mankind. Human passion for continue

progress and advancement.

(iii) Patriotism and love for country, Presence of mind

(iv) Television communication system.