# PHYSICS

PHYSICS

TOPICS : WAVE OPTICS

1. In the young’s double slit experiment, the interference pattern is found to have an intensity ratio between bright and dark fringes as 9. This implies that (a) the intensities at the screen due to two slits are 5 unit and 4 units respectively (b) the intensities at the screen due to two slits are 4 units and 1 unit respectively (c) the amplitude ratio is 9 (d) the amplitude ratio is 3

2. In an interference pattern produced by the identical coherent sources of monochromatic light. The intensity at the site of central maximum is I. If the intensity at the same spot when either of the two slits is closed is I0, we must have (a) I = I0 (b) I = 2I0 (c) I = 4I0 (d) I and I0 are not related

3. An interference pattern is observed by young’s double slit experiment. If now the separation between coherent sources is halved and the distance of screen from coherent sources is doubled; the now fringe width (a) becomes double (b) becomes one-forth (c) remains same (d) becomes four times

4. In the young’s double slit experiment, if the widths of the slits are in the ratio 49: 9; the ratio of the intensity at maxima to the intensity at minima will be (a) 169: 25 (b) 81: 16 (c) 25: 4 (d) 10: 4

5. An interference experiment is performed with blue light of wavelength 4200 A in air. If the whole set up is immersed in water of refractive index 4 / 3, then (a) The fringe will disappear (b) fringe width will remain uncharged (c) fringe width will become 4/ 3 times (d) fringe width will become 3/ 4times

6. The two slits in young’s double slit experiment are illuminated by two different sodium lamps emitting light of same wavelength (a) No interference pattern will be observed on the screen (b) interference pattern with black and white fringes is observed (c) interference pattern with yellow fringes is observed (d) interference pattern with straight line yellow fringes is observed

7. A beam light of wavelength 600 nm from a distant source falls on a single slit 1.0 mm wide and the resulting diffraction pattern is observed on a screen 2m away. The distance between the first dark fringes on either side of the central bright fringes is (a) 1.2 cm (b) 1.2 mm (c) 2.4 mm (d) 2.4 cm

8. In young’s double slit experiment the intensity of light at a point P on a screen, where the path difference between interfering rays is , is Io what is the intensity at a point Q where the path difference between interfering rays is  ? (a) (b) (c) (d) zero

9. The distance between two coherent sources is 0.1 mm. This fringe width on a screen 1.2 m away from the sources is 6.0 mm. The wavelength of light used is (a) 4000 A (b) 5000 A (c) 6000 A (d) 7200 A

10. A slit of width a is illuminated by white light. The first minimum for red light0.(  = 6500 A ) will fall at diffraction angle =30, when ‘a ‘ will be (a) 3250 A (b) 6.5 x 10-4-mm (c) 1.3 micron (d) 2.6 X 10 -6m

11. A beam of light strikes a piece of glass at an angle of incidence 60. It is found that reflected beam is completely plane polarised . Then refractive index of glass is (a) 1.5 (b) 3 (c) 2 (d) 3/2

12. The first diffraction minimum due to a single slit diffraction is at 30 for a light of wavelength . If the width of slit is 10-6m, the wavelength  is (a) 4000A (b) 5000 A (c) 1250A (d) 10,000 A

13. Rays of light fall on a glass plate of refractive index  . If the angle between reflected and refracted rays is 90; then the angle of incidence is (a) sin-1 (b) cos-1() (c) tan-1() (d) tan-1 (1/)

14. A light beam of frequency n, wavelength  travelling with velocity v in air, enters a glass slab of refractive index . . The frequency , wavelength and velocity of light beam in the glass slab will be respectively.

             (a)      	(b)  	 	(c)  	 	(d)


15. An unpolarised beam of intensity Io falls on a polaroid the intensity of emergent light is (a) (b) (c) (d) zero

16. A polarised beam falls on a Polaroid such that the optic axis of Polaroid makes an angle 600 with electric field vector of incident polarised beam. The intensity of emergent light is (a) (b) (c) (d) 17. The polarisation phenomenon can take place (a) In all waves (b) in transverse waves only (c) in longitudinal waves only (d) in standing waves only

18. Light of wavelength 6328 A is incident on a slit having a width of 0.2 mm. The width of the central maximum, measured from minimum to minimum of the diffraction pattern on a screen 9.0 m away will be about (a) 0.36 (b) 0.18 (c) 0.72 (d) 0.09

19. 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) 9I and I (c) 5I and 3I (d) 9I and 3i

20. The plane of polarisation is one which contains (a) Direction of wave propagation and direction of vibration of electric vector (b) Direction of wave propagation but perpendicular to direction of vibration of electric vector (c) Is normal to direction of wave propagation but electric field vector (d) none of above

21. The phenomenon that is exhibited by light waves but not by sound waves. (a) refraction (b) interference (c) diffraction (d) polarisation

22. White light is used to illuminate the two slits in a Young’s double slit experiment. The separation between slits is b and the screen at a distance d (>>b) from the slits. At a point on the screen directly infront of one of the slits, certain wavelengths are missing. Some of these missing wavelengths are (a) (b) (c) (d)

23. Interference was observed in interference chamber where air was present. Now the chamber is evacuated and if the same light is used , a careful observer will see (a) no interference (b) interference with bright bands (c) Interference with dark bands (d) interference with fringe width slightly increased.

24. A ray of light from a denser medium strikes a rarer medium as shown in figure. The reflected and refracted rays make an angle of 900 with each other. The angle of reflection and refraction are r and r1 respectively. The critical angle would be

(a) (b) (c) (d)

25. In two separate setups of the Young’s double slit experiment, fringes of equal width are observed when lights of wavelengths in the ratio 1:2 are used . If the ratio of the slit separation in two cases is 2:1 , the ratio of distances between the plane of slits and screen in the two setups is (a) 4:1 (b) 1:1 (c) 1:4 (d) 2:1

26. The displacements of interfering wavers are y1= 4 sint & y2 = 3 sin(t+/2) . The amplitude of the resultant wave is (a) 5 (b) 7 (c) 1 (d) zero

27. In a young’s double slit experiment, 12 fringes are obtained to be formed in a certain segment of the screen when light of wavelength 600 nm is used. If the wavelength of light is changed to 400 nm ,the number of fringes observed in the same segment of the screen is given by (a) 12 (b) 18 (c) 24 (d) 30

28. Two beams of light having intensities I and 4I interfere to produce fringe pattern on a screen. The phase difference between the beams is /2 at a point A and  at a point B . Then the difference between the resultant intensities at A and B is (a) 2I (b) 4 I (c) 5I (d) 7 I

29. A rocket is going away from earth at a speed of 0.2 c . It emits signal of frequency 4x107 Hz. The frequency of the signal as observed by an observer on earth is (a) 4x106 Hz (b) 3.2x107 Hz (c) 3x106 Hz (d) 5x107 Hz

30. The wavelength of light observed on earth from a moving star is found to decrease by 0.05%.Relative to earth , the star is (a) moving away with velocity of 1.5x105 m/s (b) moving towards with velocity of 1.5x105 m/s (c) moving away with velocity of 1.5x104 m/s (d) moving towards with velocity of 1.5x104 m/s