At the second minimum adjacent to the central maximum of a single-slit diffraction pattern the Huygens wavelet from the top of the slit is 180 ° out of phase with the wavelet from:
A)a point one-fourth of the slit width from the top
B)the midpoint of the slit
C)a point one-fourth of the slit width from the bottom of the slit
D)the bottom of the slit
E)none of these

Question

Quizplus · Accepted Answer

At the second minimum, the path difference between the wavelets from the top and bottom of the slit is equal to half the wavelength. To be in phase, the Huygens wavelet from the top of the slit needs to travel an extra distance compared to the wavelet from the midpoint of the slit. This extra distance is equal to one-fourth of the slit width. Therefore, the wavelet from a point one-fourth of the slit width from the top of the slit will be 180 degrees out of phase with the wavelet from the top of the slit.

At the Second Minimum Adjacent to the Central Maximum of a Single-Slit