Interference and Diffraction

1.Two sources are said to be coherent if

a) they produce waves of the same wavelength
b) they produce waves of the same amplitude
c) they produce waves of the same wave length having constant initial phase difference
d) they are of the same amplitude and same frequency

2.In Young double slit experiment, the ratio of the maximum to minimum intensities in the fringe system is 9 : 1. The ratio of the amplitudes of the coherent sources is

a) 9 : 1
b) 3 : 1
c) 2 : 1
d) 1 : 1

3.In Young double slit experiment, the seperation between the slits is halved and the distance between the slit and the screen doubled. The fringe width is

a)unchanged
b)doubled
c)halved
d)quadrupled

4.Two coherent sources of intersities I and 4I are superposed. The maximum and minimum possible intensities in the resultant beam is

a)5I and I
b)9I and I
c)5I and 3I
d)9I and 8I

5.In air an interference pattern produced by two identical slits the intensity at the central maximum is I. The intensity at the same spot when either of the two slits is closed is I₀. This means that

a)I =I₀
b)I = 2I₀
c)I = 3I₀
d)I = 4I₀

6.Laser light (630nm) incident on a pair of slits produces an interference pattern in which the bright fingers are seperated by 8.3 mm a second light produces interference pattern in which bright fingers are seperated by 7.6mm. The wavelength of the second light is about

a)58nm
b)580 nm
c)630 nm
d)700 nm

7.Color in a thin film results from

a)dispersion of light
b)interference of light
c)absorption of light
d)scattering of light

8.Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm. Approximately, what is the maximum distance at which these dotscan be resolved by the eye ? [ Take wavelength of light = 5000 A.U ]

a) 1 m
b) 5 m
c) 3 m
d) 6 m

9.A thin slice is cut out of a glass cylinder along a plane parallel to its axis. The slice is placed on a flat plate as shown in the figure. The observed interference fringes from this combination shall be

a) straight
b) circular
c) equally spaced
d) having fringe spacing which increases as we go outwards



10.A mixture of yellow light of wave length 580nm and blue light of wave length 450 nm is incident normally on an air film of thickness 2.9104nm. The color of the reflected light is

a)red
b)blue
c)violet
d)yellow

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

a) λ =b²/d
b) λ =2b²/d
c) λ = b²/3d
d) λ =2b²/3d

12.The first diffraction minima due to a single slit diffraction is at θ = 30° for a light of wavelength 5000 A°. The width of the slit is

a) 5 × 10 ^-5 cm
b) 10 × 10 ^-5 cm
c) 2.5 × 10 ^-5 cm
d) 1.25 × 10 ^-5cm

13.In a single slit experiment, the width of the slit is doubled. Which one of the following statement is correct?

a)the intensity and width of the central maximum are un affected
b)the intensity remains the same and the angular width becomes half
c)the intensity and angular width are both doubled
d)the intensity increases by a factor 4 and the angular width decreases by a factor 1/2.

14.In interference there is redistribution of

a)amplitude
b)frequency
c)phase
d)energy

15.To observe diffraction effects, the size of the obstacle

a) should be of the same order as the wave length of light used
b) should be much larger than the wave length
c) should exactly be 2
d) none of the above