Question

In Young's double-slit experiment, a bright spot on the screen indicates that the light coming through each slit is _____________ at that point on the screen and therefore is interfering______________

A. in phase
B. out of phase
C.constructively
D. destructively

Answer 1

Young's double slit experiment:

Constructive Interface:

To obtain constructive interference for a double slit, the path length difference must be an integral multiple of the wavelength, or

i.e. light must be in phase

Destructive Interface:

To obtain destructive interference for a double slit, the path length difference must be a half-integral multiple of the wavelength, or

​​​​​​

i.e. light must be in out of phase with 180⁰

Bright spot is formed in case of constructive interfaces

Hence Option (A) & (C) are respectively correct choices.