Question

define refraction by spherical lenses

Answer 1

the phenomenon of bending of light when it stikes a spherical lens is called refraction through spherical lens

Answer 2

Answer:

A "spherical lens" is a lens whose surface has the shape of (part of) the surface of a sphere. With the lens opened wide the image is dominated by light passing through the lens far from the center; consequently, it's the edge rays which you've adjusted the lens to bring to a sharp focus.