For Two Identical Rays of Light to Interfere Destructively,their Path

Multiple Choice

For two identical rays of light to interfere destructively,their path lengths

A) must be equal.
B) must differ by an odd number of half wavelengths.
C) must differ by an even number of half wavelengths.
D) must differ by an integral number of wavelengths.
E) need not satisfy any of these conditions.