A slit of variable width illuminated by light of wavelength λ is widened until the first order diffraction minimum moves out to a distance infinitely far away from the brightest location in the central maximum. In terms of the wavelength, the width of the slit is then
A) 0.
B) .
C) λ.
D) .
E) 2λ.

Question

A slit of variable width illuminated by light of wavelength λ is widened until the first order diffraction minimum moves out to a distance infinitely far away from the brightest location in the central maximum. In terms of the wavelength, the width of the slit is then
A) 0. 
B) . 
C) λ. 
D) . 
E) 2λ.

Quizplus · Accepted Answer

When the first order diffraction minimum moves out to infinitely far away, the angle of diffraction becomes 90 degrees. Using the equation for single slit diffraction, sinθ = λ/d, we see that d = λ/sinθ = λ/1 = λ. Therefore, the width of the slit is equal to the wavelength of the light. Therefore, the correct answer is (C).

A Slit of Variable Width Illuminated by Light of Wavelength