#### 12 Standard English medium Physics Reduced syllabus Public Exam Model Question Paper - 2021

12th Standard

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Physics

Time : 02:45:00 Hrs
Total Marks : 70

Part I

Choose the most suitable answer from the given four alternatives and write the option code with the corresponding answer.

15 x 1 = 15
1. An electric dipole is placed at an alignment angle of 300 with an electric fi eld of 2 × 105 NC-1. It experiences a torque equal to 8 N m. Th e charge on the dipole if the dipole length is 1 cm is

(a)

4 mC

(b)

8 mC

(c)

5 mC

(d)

7 mC

2. Two identical conducting balls having positive charges q1 and q2 are separated by a center to center distance r. If they are made to touch each other and then separated to the same distance, the force between them will be

(a)

less than before

(b)

same as before

(c)

more than before

(d)

zero

3. Two identical coils, each with N turns and radius R are placed coaxially at a distance R as shown in the fi gure. If I is the current passing through the loops in the same direction, then the magnetic field at a point P which is at exactly at$\frac { R }{ 2 }$ distance between two coils is

(a)

$\frac { 8N{ \mu }_{ ° }I }{ \sqrt { 5 } R }$

(b)

$\frac { 8N{ \mu }_{ ° }I }{ { 5 }^{ \frac { 3 }{ 2 } }R }$

(c)

$\frac { 8N{ \mu }_{ ° }I }{ { 5 }R }$

(d)

$\frac { 4N{ \mu }_{ ° }I }{ \sqrt { 5 } R }$

4. A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic fi eld B, as shown in the fi gure.

The potential diff erence developed across the ring when its speed v, is

(a)

Zero

(b)

$\frac { { Bv\pi { r }^{ 2 } } }{ 2 }$and P is at higher potential

(c)

πrBv and R is at higher potential

(d)

2rBvand R is at higher potential

5. An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω are connected in series across a source of emf v = 10 sin 340 t. The power loss in AC circuit is

(a)

0.76 W

(b)

0.89 W

(c)

0.46 W

(d)

0.67 W

6. The electric and magnetic fields of an electromagnetic wave are

(a)

in phase and perpendicular to each other

(b)

out of phase and not perpendicular to each other

(c)

in phase and not perpendicular to each other

(d)

out of phase and perpendicular to each other

7. When a metallic surface is illuminated with radiation of wavelength λ, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2λ, the stopping potential is $\frac{V}{4}$. The threshold wavelength for the metallic surface is

(a)

(b)

(c)

$\frac{5}{2}λ$

(d)

8. The nucleus is approximately spherical in shape. Then the surface area of nucleus having mass number A varies as

(a)

A2/3

(b)

A4/3

(c)

A1/3

(d)

A5/3

9. The principle used for 'transmission of light signals through optical fibre is ________.

(a)

refraction

(b)

diffraction

(c)

polarisation

(d)

total internal reflection

10. In actual practice, the range of uplink frequencies used is _________ GHz.

(a)

5.725 - 7.075

(b)

3.4 - 4.8

(c)

6 - 10

(d)

9 - 10

11. Heavily doped region of a transistor is ___________

(a)

base

(b)

emitter

(c)

collectorresistor

(d)

resistor

12. Supplier of majority charge carriers in a transistor is ______

(a)

emitter

(b)

base

(c)

collector

(d)

resistor

13. Acceptor of majority charge carriers in a transistor is ___________

(a)

emitter

(b)

base

(c)

collector

(d)

resistor.

14. Ihecollector-base junction of a transistor offers _________ resistance to current

(a)

low

(b)

high

(c)

zero

(d)

moderate

15. ln NPN transistors, when the emitter-base junction is forward-biased, the direction of conventional current is from _____________

(a)

base to emitter

(b)

emitter to base

(c)

collector to base

(d)

base to collector

16. Part II

Answer any 6 questions. Question no. 16 is compulsory.

6 x 2 = 12
17. Define electrical conductivity of a conductor. On what factor does it depend?

18. Which ray has high ionising power? Why?

19. What is meant by correspoding points?

20. What is forbidden energy gap?

21. What is conduction band?

22. What is transducer?

1. Part III

Answer any 6 questions. Question no.27 is compulsory.

6 x 3 = 18
23. What is the radius of the illumination when seen above from inside a swimming pool from a depth of 10 m on a sunny day? What is the total angle of view? [Given, refractive index of water is 4/3]

24. If the focal length is 150 cm for a glass lens, what is the power of the lens?

25. Calculate the average atomic mass of chlorine if no distinction is made between its different isotopes?

26. Discuss the applications of Nanomaterials in various fields

27. Explain the construction and working of a full wave rectifier.

28. State Boolean laws. Elucidate how they are used to simplify Boolean expressions with suitable example.

1. Part IV

5 x 5 = 25
29. Write the application of alpha decay in smoke detectors.

30. Express one joule in eV. Taking 1 amu = 931 MeV. Calculate the mass of C-12 atom.

31. You are given two converging lenses of focal lengths 1.25 cm and 5 cm to design a compound microscope. If it is desired to have a magnification of 30, find out the seperation between the objective and the eyepiece

32. In Young's experiment, the upper slit is covered by a thin glass plate of refractive index 1.4 while the lower slit is covered by another glass plate having the same thickness as the first one but having refractive index 1.7. Interference pattern is observed using light of wavelength 5400A . It is observed that the point P on the screen where the central maximum (n = 0) fell before the glass were inserted now has $\cfrac { 3 }{ 4 }$ th original intensity. It is further observed that what used to be the fifth maximum earlier, lies below the point P while the sixth minimum lies above P. Calculate the thickness of the glass plate.

33. For a BJT circuit shown, assume that the 'β' of the transistor is very large and VBE= 0.7 V. The mode of operation.