A single slit is located effectively at infinity in front of a lens of focal length Im and it is illuminated normally with light of wavelength 6000A. The first minima on either side of central maximum are separated by 4 mm. Width of the slit is ......:

Options

A. A)`0.1 mm`
B. B)0.2 mm`
C. C)0.3 mm`
D. D)0.4 mm`

Answer

C

Explanation

`e sin theta = lamda implies sin theta ~~ theta = ( lamda )/(e)`
`therefore x= f, theta = f lamda // e`
`therefore` 2x = separation between minima on either side of central maximum
`= (2f lamda)/(e) `
Hence `e = ( 2 f lamda )/(2x) = ( 2 xx 1 xx 600 xx 10 ^(-9))/( 4 xx 10 ^(-3)) = 0.3 mm`