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 riven below:

B and D only

CONDITIONS FOR SUSTAINED INTERFERENCE:

1. The two interfering sources must be coherent

2. The interfering waves should have equal amplitude

3. The two interfering waves must be propagated along the same line 

4. The separation between the two sources must be as small as possible. 

5. The two sources must be narrow.

6. If the interfering waves are polarised, they must be in the same state of polarisation