Question

define principal focus of spherical lens and spherical mirror

Answer 1

Principal focus is the point where the rays of light meet at a point and forms the image of the object.
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Answer 2

Principle focus - The rays coming parallel to principle axis after reflection from the lens meet at a point or appear to meet at a point on principal axis. This is called 'Principle focus of spherical lens'.

Spherical mirror - A hollow spherical piece of mirror which is painted from one side and polished from one side, is called spherical mirror.

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