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 minima is at a distance of 2.5 mm from the centre of the screen. The width of the slit is:

• A. 0.2 mm
• B. 1 mm
• C. 2 mm
• D. 1.5 mm

Answer 1

Answer: (A)

0.2 mm

Width of slit,
$d=\frac{n\lambda D}{x}$
Here, $n=1,D=1m,x=2.5\times {10}^{-3}m$

$\lambda =500nm=500\times {10}^{-9}m$

$\therefore d=\frac{1\times 500\times {10}^{-9}\times 1}{2.5\times {10}^{-3}}=2\times {10}^{-4}m=0.2mm$