Question

A ray of light, after refraction through a concave lens emerges parallel to the principal axis.

1. Draw a ray diagram to show the incident ray and its corresponding emergent ray.
2. The incident ray when produces meets the principal axis at a point F. Name the point F.

Answer 1

1. AB and A' B' are incident rays
   BC and B' C' are emergent rays.
   

2. The first focus is on the location where the incident ray produced meets the primary axis.