Consider sunlight incident on a pinhole of widht `10^(3)Å`. The image of the pinhole seen on a screen shall be

Options

A. a sharp white ring.
B. different from a geometrical image
C. a diffused central spot, white in colour.
D. diffused coloured region around a sharp central white spot.

Answer

B, D

Explanation

Average wavelength of visible light in Sunlight is `lamda=6000Å` and here width of slit is `d=1000Å`
`(lamda)/(d)=(6000)/(1000)=6implies(lamda)/(d)gtgtgtgt1`
Amount of diffraction would be very large. Hence image would appear different than geometrical image. Thus option (B) is correct.
In the present case, at the central point on the screen, constituent colours of white light superpose with equal proportion and produce constructive interference to give white coloured spot at the central position. But as we move away from centre, on the successive rings, constructive interference takes place for different colours (in the order from blue to red) and so different colours are dominant in different rings (with very small amounts for remaining colours). Thus, region around central white spot appears to be colourful in which as the order of maximum increases, intensity of light goes on decreasing. It means this region diffuses as we move away from centre. Thus, option (D) is also correct.