Question:
A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1 m away. It is observed that the
first minimum is at a distance of 2.5 mm from the centre of the screen. Find the width of the slit.
Solution:
Wavelength of the beam of light, λ = 500 nm
Distance between the slit and the screen, D= 1 m
Distance of the first minimum from the centre of the screen, x = 2.5 mm = 2.5 x 10-3 m
First minima, n = 1
Consider the equation, nλ = xd/D
⇒ d = nλD/x = ( 1 x 500 x 10-9 x 1) /( 2.5 x 10-3 )
= 200 x 10-6 m