State the essential conditions for two light waves to be cohrent.

State two conditions for two light sources to be coherent. Derive an expression for the fringe width in Young.s double slit experiment for interfernce with suitable diagram.

What is the essential condition for addition of two vectors?

What is the essential condition for observing rainbow ?

What is total internal reflection of light ? What are the two essential conditions for total internal reflection to take place ?

What is the essential condition for observing a rainbow?

State the necessary condition for diffraction of light to occur?