A parallel beam of monochromatic light is incident on a slit of width 2 cm. The light passing through the slit falls on a screen 2 m away. As the slit width is decreased:
A) the width of the pattern on the screen continuously decreases
B) the width of the pattern on the screen at first decreases but then increases
C) the width of the pattern on the screen increases and then decreases
D) the width of the pattern on the screen remains the same
E) the pattern on the screen changes color going from red to blue

Question

Quizplus · Accepted Answer

According to the diffraction theory, as the slit width decreases, the width of the pattern on the screen at first decreases but then starts to increase due to the increasing influence of diffraction. This means that initially the pattern becomes sharper, but as the slit becomes very narrow, the pattern becomes wider again. Therefore, option B is the correct answer. Option A and D are not correct, as the width of the pattern changes with a changing slit width. Option C is incorrect, as the pattern does not first increase and then decrease. Option E is irrelevant, as there is no mention of any color change in the question.

A Parallel Beam of Monochromatic Light Is Incident on a Slit