Question

what is refraction& what do u mean by power of a lens?

Answer 1

When light passes from one optical medium to another optical medium ,its speed changes due to which its path changes.this phenomenon is regarded as refraction.
The degree of convergence and divergence of light rays passing through the lens is called power.

Answer 2

Refraction-
The bending of a ray when it passes at an angle from one medium into another in which its speed is different.

Power of Lens-
The ability of a lens to converge/diverge a beam of light rays is expressed in terms of its power.

Hope this helps.....