Question

Define - Focal length and Principal focus.

Answer 1

Answer:

The distance between the centre of a mirror or a length and it's focus is called focal length.Principal focus is a point on focal plane and is located on principle axis.

Answer 2

Answer:

• The distance of the principle focus center of the lens us known as focal length.

• The first principle focus of the lens is the positive of the object on the principle axis of the lens.

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