Question

differentiate between principal focus and Focal length..?​

Answer 1

Answer:

Principal focus is a point (on the principal axis) where parallel incident rays meet after reflecting (in mirrors) or refracting (in lenses). ... Principal Focus also determines the focal length of the lens/mirror. Focus is just a random point where some rays meet, it might be at the principal focus or otherwise.

Explanation:

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Answer 2

Answer:

Focus is the point on the principal Axis where the reflected rays meet or intersect whereas focal length is the distance between the pole and the focus. Focal length is always negative in case of concave mirrors but always positive in case of convex mirrors.