Question

In the ray diagrams of spherical lenses,refraction of the incident light ray is occuring once.But light has to be refracted twice by the two spherical surfaces.

Answer 1

The lens has two spherical surfaces. Light is refracted twice before it comes out of the lens. When entering into the lens ( from rarer to denser ) and when coming out of the lens ( from denser to rarer ).The difference in the deviation by the two surfaces is less to observe.