Question

What is the half angular width of the central bright maximum in the Fraunhofer diffraction pattern of a slit of width 12 X 10^-7m when the slit is illuminated by monochromatic light of wavelength 6000 Å.

(a) 20°

(b) 30°

(c) 40°

(d) 50°

This question was addressed to me during an online interview.

My question is from Fraunhofer Diffraction in chapter Optics of Engineering Physics II

Answer 1

Correct choice is (b) 30°

Easy explanation: We know sin θ =\(\frac{\lambda}{a}\), where θ is the half angular width of the central maximum.

 Given:     a = 12 X 10^-7 m, λ = 6000 Å = 6.0 X 10^-7 m

sinθ = \(\frac{\lambda}{a}\) = 0.5 = 30°

 Thus, the half angular width of the central bright maximum is 30°.