The interference pattern is said to be sustained if the position and intensity of fringes remain same throughout on the screen. For sustained interference:

A. The size of slits must be large.

B. Two sources must be coherent.

C. Screen must be very close to slits.

D. Separation between the slits must be small.

E. The screen must be placed close to the plane of slits.

Choose the correct answer from the options given below:

B and D only

Conditions for sustained interference pattern:

 1. The two sources of light must be coherent with same frequency or wavelength and with same phase or constant phase difference.

2. The two sources should preferably have the same amplitude.

3. The two sources must be very close to each other.

4. The sources should emit light waves continuously.