A parallel beam of coherent light of wavelength λ is incident on a rectangular slit of width d. After passing through the slit the light is incident on a screen a distance D from the slit where D is much greater than d. What is the width of the central maximum of the diffraction pattern as measured on the screen?

A. \(\frac{{2D\lambda }}{d}\)

B. \(\frac{{2d}}{{D\lambda }}\)

C. \(\frac{{D\lambda }}{d}\)

D. \(\frac{d}{{D\lambda }}\)

A

It is logical that as D increases so the width of the central maximum will increase. Hence B and D (both with D on the denominator) can be eliminated. A sketch of the graph of the diffraction pattern for a single slit will show that A is correct.