#### 12th Standard Physics English Medium Reduced Syllabus Important Questions with Answer key - 2021 Part - 2

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 100

Multiple Choice Questions

10 x 1 = 10
1. What physical quantities may X and Y represent? [Y represents the first mentioned quantity].

(a)

K.E - velocity of a particle

(b)

pressure - temperature of a given gas (constant volume)

(c)

capacitance - charge to give a constant potential

(d)

potential - capacitance to give a constant charge

2. Which one of the following pair of particles move with same velocity along the same circular path in a uniform magnetic field?

(a)

electron, proton

(b)

proton, deutron

(c)

proton, alpha particle

(d)

deutron, alpha particle

3. This works on the principle of Tangent Law

(a)

Tangent Galvanometer

(b)

Galvanometer

(c)

Potentiometer

(d)

Metre Bridge

4. An α-particle enters a magnetic field of 1T with a velocity 106 m/s in a direction perpendicular to the field. The force on α-particle is

(a)

1.6 x 10-13N

(b)

6.4  x 10-13N

(c)

4.8  x 10-13N

(d)

3.2  x 10-13N

5. Which of the following electromagnetic radiation is used for viewing objects through fog

(a)

microwave

(b)

gamma rays

(c)

X- rays

(d)

infrared

6. The velocity of light is maximum in

(a)

Diamond

(b)

Water

(c)

Vacuum

(d)

Glass

7. If Vg, Vx' Vm are speeds of gamma rays, X rays and microwaves respectively in vacuum, then

(a)

Vg<Vx<Vm

(b)

Vg>Vk>Vm

(c)

Vg > Vx < Vm

(d)

Vg=Vx=Vm

8. When a material particle of rest mass m0, attains the velocity of light. its mass becomes

(a)

0

(b)

2 m0

(c)

4 m0

(d)

9. Which of the following two form a pair in pair-production?

(a)

electron and positron

(b)

proton and positron

(c)

electron and neutron

(d)

neutron and positron

10. The change in the resting frequency of a FM transmitter is called ________

(a)

frequency swing

(b)

frequency deviation

(c)

range offrequency

(d)

centre deviation

11. 2 Marks

15 x 2 = 30
12. Distinguish between drift velocity and mobility.

13. Define draft velocity and write its relationship with the current flowing through it

14. What are LC oscillations?

15. (i) How is the speed of Electromagnetic waves in vacuum determined by the electric and magnetic fields? and
(ii) Do Electromagnetic waves carry energy and momentum?

16. Write a note on optical fibre.

17. State the laws of reflection

18. Derive the relation between f and R for a spherical mirror.

19. Is there any difference between coloured light obtained from prism and colours of soap bubble?

20. What is meant by concave and convex mirror?

21. Write the two conditions for total internal reflection.

22. Define angle of deviation d.

23. Write the properties of cathode rays.

24. Discuss about Nicol prism.

25. What is the use of an erecting lens in a terrestrial telescope?

26. Write the difference of real and virtual images by a plane mirror.

27. 3 Marks

15 x 3 = 45
28. Discuss the basic properties of electric charges.

29. A coil of a tangent galvanometer of diametre 0.24 m has 100 turns. If the horizontal
component of Earth’s magnetic field is 25 × 10-6 T then, calculate the current
which gives a deflection of 60o.

30. Two identical charged protrudes moving with the same speed enter a region of uniform magnetic field. If one of these enters normal to the field direction and the other enters along a direction at 30° with the field. What would be the ratio of their angular frequencies.

31. Give and explain the mechanical analogy of LC oscillations by qualitative treatment.

32. Name the parts of Electromagnetic spectrum which is
(i) used to destroy becteria.
(ii) produced by where is a sudden deceleration of high speed electrons.
(iii) used in food industry.

33. Derive the mirror equation and the equation for lateral magnification.

34. Describe the Fizeau's method to determine speed of light.

35. Derive the equation for acceptance angle and numerical aperture, of optical fiber.

36. A thin rod of length f /3 is placed along the optical axis of a concave mirror of focal length f such that its image which is real and elongated just touches the rod. Calculate the longitudinal magnification.

37. Light travels from air in to glass slab of thickness 50 cm and refractive index 1.5.
(i) What is the speed of light in glass?
(ii) What is the time taken by the light to travel through the glass slab?
(iii) What is the optical path of the glass slab?

38. The angle of minimum deviation for a prism is 37o. If the angle of prism is 60o, find the refractive index of the material of the prism.

39. What is principal axis of the mirror?

40. Write the difference between paraxial rays and marginal rays.

41. What is thin lens?

42. (a) Show that the ratio of velocity of an electron in the first Bohr orbit to the speed of light c is a dimensionless number
(b) Compute the velocity of electrons in ground state, first excited state and second excited state in Bohr atom model.

43. 5 Marks

15 x 5 = 75
44. Two conducting spheres of radius r1 = 8 cm and r2 = 2 cm are separated by a distance much larger than 8 cm and are connected by a thin conducting wire as shown in the figure. A total charge of Q = +100 nC is placed on one of the spheres. After a fraction of a second, the charge Q is redistributed and both the spheres attain electrostatic equilibrium.

(a) Calculate the charge and surface charge density on each sphere.
(b) Calculate the potential at the surface of each sphere.

45. Suppose a charge +q on Earth’s surface and another +q charge is placed on the surface of the Moon. (a) Calculate the value of q required to balance the gravitational attraction between Earth and Moon (b) Suppose the distance between the Moon and Earth is halved, would the charge q change?
(Take mE = 5.9 × 1024 kg, mM = 7.9 × 1022 kg)

46. An electric dipole of length 4cm, when placed with its axis making an angle of 60° with a uniform electric field, experiences a torque of 4√3 Nm. Calculate the potential energy of the dipole, if it has charge ±8nC.

47. In a metre bridge the balancing length is found to be 40 cm from end A. If a resistance of 10 $\Omega$ is connected in series with R, balanceing length is obtained 60 em from A. calculate the valueR&S.

48. An electron moving perpendicular to a uniform magnetic field 0.500 T undergoes circular motion of radius 2.80 mm. What is the speed of electron?

49. Two singly ionized isotopes of uranium $_{ 92 }^{ 235 }{ U\quad and\quad _{ 92 }^{ 238 }{ U } }$ (isotopes have same atomic  number but different mass number) are sent with velocity 1.00 × 105 m s-1 into a magnetic field of strength 0.500 T normally. Compute the distance between the two isotopes after they complete a semi-circle. Also compute the time taken by each isotope to complete one semi-circular path. (Given: masses of the isotopes: m235 = 3.90 x 10-25 kg and m238 = 3.95 x 10-25 kg)

50. Explain mechanical analogy ofLC oscillations by quantitative treatment.

51. An electromagnetic wave is traveling in vacuum with a speed 3 x 108 m/s. find its velocity in a medium having relative electric and magnetic permeability 2 and 1respectively.

52. An object is placed in front of a concave mirror of focal length 20 cm, The image formed is three times the size of the object. Calculate two possible distances of the object from the mirror.

53. What is the angle at which a glass plate of refractive index 1.65 is to be kept with respect to the horizontal surface so that an unpolarised light travelling horizontal after reflection from the glass plate is found to be plane polarised?

54. (I) For a glass ( $\mu =\sqrt { 5 }$) the angle of minimum deviation is equal to the angle of the prism. Find the angle ofthe prism.
(ii) Draw ray diagram when incident ray falls normally on one of the two equal sides of a right angled isosceles prism having refractive inded $\mu =\sqrt { 3 }$.

55. Derive the equation for lateral magnification in spherical mirrors.

56. Calculate the cut-off wavelength and cut-off frequency of x-rays from an x-ray tube of accelerating potential 20,000 V.

57. Write the application of x-rays

58. Prove the laws of reflection using Huygen's principle.