In Young's experiment, using red light (A = 6600 $\stackrel{\circ }{\mathrm{A}}$ ), 60 fringes are seen in the field of view. How many fringes will be seen by using violet light (A = 4400 $\stackrel{\circ }{\mathrm{A}}$) ?

• 10

• 20

• 45

• 90

42.

The apparent frequency of the whistle of an engine changes in the ratio 9 : 8 as the engine passes a stationary observer. If the velocity of the sound is 340 ms^-1, then the velocity of the engine is 

• 40 ms^-1

• 20 ms^-1

• 340 ms^-1

• 180 ms^-1

The width of a single slit if the first minimum is observed at an angle 2° with a light of wavelength 6980 $\stackrel{\circ }{\mathrm{A}}$

• 0.2 mm

• 2 × 10^-5 mm

• 2 × 10⁵ mm

• 2 mm

In the Young's double slit experiment, the central maxima is observed t0 be I₀. If one of the slits is covered, then the intensity at the central maxima will become

• $\frac{{\mathrm{I}}_0}{2}$

• $\frac{{\mathrm{I}}_0}{\sqrt{2}}$

• $\frac{{\mathrm{I}}_0}{4}$

• I₀

A single slit is located effectively at infinity in front of a lens of focal length 1 m and it is illuminated normally with light of wavelength 600 nm. The first minima on either side of central maximum are separated by 4 mm. Width of the slit is

• 0.1 mm

• 0.2 mm

• 0.3 mm

• 0.4  mm

In Young's double slit experiment, the width of one of the slits is slowly increased to make it twice the width of the other slit. Then in thei nterference pattern 

• the intensity of maxima increase while that of minima decrease

• the intensities of both maxima and minima decrease

• the intensities of both maxima and minima increase

• the intensity of maxima decrease while that of minima increase

Two coherent sources whose intensity ratio is 81 : 1 produce interference fringes. The ratio of minimum to maximum intensity, i,e I_min : I_max is

• 16 : 25

• 9 : 1

• 1 : 9

• 25 : 16

Huygen's principle of secondary wavelets may be used to

• find the velocity of light in vacuum

• explain the particle behaviour of light

• find the new position of a wavefront

• explain photoelectric effect

In Young's double slit experiment, the intensity of light coming from one of the slits is double the intensity from the other slit. The ratio of the maximum intensity to the minimum intensity in the interference fringe pattern observed is

• 34

• 40

• 25

• 38

In Young's double slit experiment, the fringe width is β, if the entire arrangement is placed in a liquid of refractive index n, the fringe width becomes

• nβ

• $\frac{\mathrm{\beta }}{\mathrm{n} + 1}$

• $\frac{\mathrm{\beta }}{\mathrm{n} - 1}$

• $\frac{\mathrm{\beta }}{\mathrm{n}}$