CHAPTER 9 PHYSICAL OPTICS

 

9.1      Multiple choice questions

1.      Who presented the corpuscle theory of light?
(a) Huygen	(b) Newton
(c) Young	(d) Maxwell
2.      Which phenomenon does not explain the of wave theory of light?
(a) Polarization	(b) Interference
(c) Diffraction	(d) Compton effect
3.      Interference of lights occur when their source is;
(a) Monochromatic	(b) Coherent
(c) Closed to each other	(d) All of these
4.      In young’s double slit experiment, when the distance between two slits is halved and distance between slits and screen is doubled then the fringe width is:
(a) Remain same	(b) Halved
(c) Doubled	(d) Quadrupled
5.      In young double slit experiment, the ratio of fringe width of bright to dark fringe is
(a) 1:1	(b) 1:2
(c) 2:1	(d) 2:3
6.      In the Young’s double slit experiment if white light is used
(a) Bright fringes will be seen	(b) Dark fringes will be seen
(c) Alternate dark and bright fringes will be seen	(d) No interference fringes will be seen
7.      When light is reflected from dense medium to rare medium then its path
(a) Remains same	(b) Changes by λ/2
(c) changes by λ	(d) Changes by 3λ/2
8.      Michelson interferometer is an optical instrument which is being used for the measurement of;
(a) Velocity	(b) Frequency
(c) Amplitude	(d) Wavelength
9.      Mathematical condition of destructive interference in thin film is;
(a) mλ	(b)mλ/2
(c) (m+1/2)λ	(d) (m+λ)
10.  Which parameter of light does not change when light is reflected from dense
(a) Frequency	(b) Wavelength
(c) Velocity	(d) Amplitude
11.  In Michelson interferometer, a fringe is changed by changing the position of movable mirror at a distance
(a) λ/4	(b) λ/2
(c) λ	(d) 2λ
12.  Number of slits in a diffraction grating depends upon.
(a) Speed of light	(b) Frequency of light
(c) Wavelength of light	(d) Amplitude of light
13.  If the wavelength of the incident x-rays is 2 x 10-10 m then the required number of slits per centimeter for its diffraction should be
(a) 5 x 106	(b) 5 x 107
(c) 5 x 108	(d) 5 x 1010
14.  Which phenomenon has confirmed that light is transverse wave.
(a) Interference	(b) Diffraction
(c) Reflection	(d) Polarization
15.  If the unpolarized incident light with intensity ‘I’ is polarized to polaroid sheet, then the intensity of plane polarized light will be;
(a) I/2	(b) √I
(c) I	(d)2I
16.  Which one of the following cannot be polarized.
(a) X-rays	(b) Radio waves
(c) Ultraviolet waves	(d) Sound waves

 

Answers

1. (b) Newton
2. (d) Compton effect
3. (d) All of these
4. (a) Remain same
5. (a) 1:1
6. (d) No interference fringes will be seen
7. (b) Changes by 
8. (d) Wavelength
9. (a)  mλ
10. (a) Frequency
11. (b) λ/2
12. (c) Wavelength of light
13. (b) 5 x 10⁷
14. (d) Polarization
15. (a) I/2
16. (d) Sound waves

9.2      Short question

14. Can visible light produce interference fringes?

ans.    Yes, visible light can produce interference fringes if source of visible light is coherent and monochromatic.

15. In Young’s double slit experiment, one of the slits is covered with blue filter and the other with red filter. What would be the pattern of light intensity on the screen?

ans.    Pattern would not be form on the screen because red light and blue light have different frequencies (not coherent source ).

16. State whether the fringe width for bright and dark fringes in Young's interference always constant?

17. Find the grating element of the diffraction grating containing 2000 lines/cm?

9.3      Numerical problems

1. Light of wavelength 400nm is allowed to illuminate the slits of Young’s experiment. The separation between the slits is 0.10m m and the distance of the screen from the slits where interference effects are observed is 20 cm. At what angle the first minimum will fall? What will be the linear distance on the screen between adjacent maxima?

3. Interference fringes were produced by two slits spaced 0.2mm apart, on a screen at a distance of 150 cm from the slits, the third bright fringe is found to be displaced 7.5mm from the central fringes. What is the wavelength of light producing the fringes?

4. Green light of wavelength 540nm is diffracted by grating having 2000 lines/cm. (a) Compute the angular deviation of the third order image. (b) Is 12^th order image possible?

8. Calculate the distance through which the mirror of the Michelson Interferometer has to be displaced between two consecutive positions of maximum distinctness of D₁ and D₂ lines of sodium. The wavelength of D₁ line is 5890Å and of D₂ line is 5896 Å.