Question 1 Page 168 - Chapter 10 Class 10 - Light - Reflection and Refraction

Define the principal focus of a concave mirror.

Answer

The point at which 

rays parallel to principal axis

coming from infinity converge 

after being reflected from concave mirror 

is called the principal focus of concave mirror.

For a convex mirror

The point at which 

rays parallel to principal axis

coming from infinity appear to converge 

after being reflected from convex mirror 

is called the principal focus of convex mirror.