In Young's experiment, how must waves be vibrating to for interference to occur?

A. in line

B. in phase

C. out of phase

D. out of line

The phenomenon of the superposition of two waves is called the interference of the wave.

For a stable and clear interference pattern, the conditions can be:

The sources must be coherent i. e. the phase difference between the waves must be constant. There should be a monochromatic source of light.

So, it is clear from the first condition that the waves must be vibrating in phase to occur interference.

Hence, the correct option is (b) "in phase".

The answer is B. In Phase