Question

The diffraction pattern of a light of wavelength 400 nm diffracting from a slit of width 0.2 mm is focused on the focal plane of a convex lens of focal length 100 cm. The width of the 1st secondary maxima will be :

• A. 2 mm
• B. 2 cm
• C. 0.02 mm
• D. 0.2 mm

Answer 1

The Correct Option is A

The width of the first secondary maxima for single-slit diffraction is given by:

Width of 1^st secondary maxima = \( \frac{\lambda D}{a} \)

where \( \lambda = 400 \times 10^{-9} \, \text{m} \), \( a = 0.2 \times 10^{-3} \, \text{m} \), and \( D = 100 \, \text{cm} = 1 \, \text{m} \). Substitute the values:

Width of 1^st secondary maxima = \[ \frac{400 \times 10^{-9} \times 1}{0.2 \times 10^{-3}} = 2 \, \text{mm} \]