#### 12th Standard Physics English Medium Wave Optics Reduced Syllabus Important Questions With Answer Key 2021

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 100
Multiple Choice Questions
10 x 1 = 10
1. A plane glass is placed over a various coloured letters (violet, green, yellow, red) The letter which appears to be raised more is,

(a)

red

(b)

yellow

(c)

green

(d)

violet

2. In a Young’s double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing on the screen, the screen-to-slit distance D must be changed to,

(a)

2D

(b)

$\frac{D}{2}$

(c)

$\sqrt{2}$D

(d)

$\frac{D}{\sqrt2}$

3. Two coherent monochromatic light beams of intensities I and 4I are superposed. The maximum and minimum possible intensities in the resulting beam are

(a)

5I and I

(b)

5I and 3I

(c)

9I and I

(d)

9I and 3I

4. When light is incident on a soap film of thickness 5×10–5 cm, the wavelength of light reflected maximum in the visible region is 5320 Å. Refractive index of the film will be,

(a)

1.22

(b)

1.33

(c)

1.51

(d)

1.83

5. First diffraction minimum due to a single slit of width 1.0×10–5 cm is at 30o. Then wavelength of light used is,

(a)

400 $\mathring { A }$

(b)

500 $\mathring { A }$

(c)

600 $\mathring { A }$

(d)

700 $\mathring { A }$

6. A ray of light strikes a glass plate at an angle 60o. If the reflected and refracted rays are perpendicular to each other, the refractive index of the glass is,

(a)

$\sqrt3$

(b)

$\frac{3}{2}$

(c)

$\sqrt{\frac{3}{2}}$

(d)

2

7. One of the of Young’s double slits is covered with a glass plate as shown in figure. The position of central maximum will,

(a)

get shifted downwards

(b)

get shifted upwards

(c)

will remain the same

(d)

data insufficient to conclude

8. Light transmitted by Nicol prism is,

(a)

partially polarised

(b)

unpolarised

(c)

plane polarised

(d)

elliptically polarised

9. The transverse nature of light is shown in,

(a)

interference

(b)

diffraction

(c)

scattering

(d)

polarisation

10. A rear mirror of a vehicle is cylindrical having radius of curvature 10 cm. The length of arc of curved surface is also 10 cm. If the eye of driver is assumed to be at large distance, from the mirror, then the field of view in radian is

(a)

0.5

(b)

1

(c)

2

(d)

4

11. 2 Marks
10 x 2 = 20
12. What is Rayleigh's scattering?

13. What is the significance of electromagnetic wave theory of light?

14. Write a short note on quantum theory of light.

15. What is interference of light?

16. Differentiate between polarised and unpolarised light.

17. State Brewster's law.

18. What is myopia? What is its remedy?

19. What is hypermetropia? What is its remedy?

20. Does the magnifying power of a microscope depend on the colour of the light used? Justify your answer,

21. Which of the following waves can be polarized
(i) Heat waves
(ii) Sound waves? Give reason to support your answer

22. 3 Marks
10 x 3 = 30
23. Prove law of reflection using Huygens' principle.

24. Prove law of refraction using Huygens' principle.

25. Explain the Young's double slit experimental setup and obtain the equation for path difference.

26. Discuss diffraction at single slit and obtain the condition for nth minimum.

27. Discuss the diffraction at a grating and obtain the condition for the mth maximum.

28. Obtain the equation for resolving power of optical instrument.

29. Discuss about simple microscope and obtain the equations for magnification for near point focusing and normal focusing.

30. Discuss about astronomical telescope.

31. Mention different parts of spectrometer and explain the preliminary adjustments.

32. What is Airy's discs

33. 5 Marks
8 x 5 = 40
34. A beam of light of wavelength 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. What is the distance between the first dark fringe on either side of the central bright fringe?

35. The critical angle for a given piece of glass is 45°. Calculate the polarising angle for it. Also calculate the angle of refraction when light is incident on this glass at an angle of incident equal to ip.

36. A Parallel beam of light of 500 nm falls on a narrow slit and be resulting diffraction pattern is observed on a screen 1m away. It is observed that the first minimum is at a distance of 2.5 mm from the centre of the screen. Calculate the width of the slit.

37. In Young's double slit experiment monochromatic ligt of wavelength 630 nm illuminates the pair of slits and produces an interference pattern in which two consecutive bring fringes are separated by 8.1 mm. Anther source of monochromatic light produces the interference pattern in which the two consecutive bright fringes are separated by 7.2 mm. Find the wavelength of light from the second source. What is the effect on the interference fringes in the monochromatic source is replaced by a source of white light?

38. If the focal lengths of the objective and eyepiece of a microscope are 2 cm and 5 cm and 5 cm respectively and the distance between them is 20 cm, what is the distance of the object from the objective when the image seen by the eye is 25 cm from eyepiece? Also find the magnifying power.

39. The eyepiece 'and objective of a microscope having focal lengths of 0.03 m and 0.04 m respectively are separated by a distance 0.2 m. Now the eyepiece and the objective are to be interchanged such that the angular magnification of the instrument remains the same. What is the separation between the lenses?

40. Light of wavelength 5000 Å falls on a plane reflecting surface. What are the wavelength and frequency of reflected light? For what angle of incidence is the reflected ray normal to the incident ray?

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