Question

what is principal focus

Answer 1

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PRINCIPAL FOCUS IS A RAY IN WHICH COLLIMATED LIGHT RAY PARALLEL TO THE AXIS OF FOCUS

Answer 2

Answer:

The point on the principal axis where the parallel rays of light converge after reflection ( in case of concave mirror) or appear to diverse from that point ( in case of convex mirror) us called principal focus.

Explanation:

The distance from the origin and principal focus is called focal length and it is denoted by ' f'.

now , R is the radius of curvature then

f = R/2 or

R = 2f