Is the relation between focal length and radius of curvature valid for lens ?

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Solution

Focal length (f) is the distance from mirror at which the light rays coming parallel from infinity meet.
Radius of Curvature R is the radius of the sphere of which the mirror is a part.
Focal length and radius of curvature are related as:
$\frac{R}{2}$ ( for paraxial ray)
This is valid for mirrors.
in case of lenses
$\frac{1}{f} = (μ_{r} - 1) {\frac{1}{R_{1}} - \frac{1}{R_{2}}}$
therefore both formulas for mirror and lenses are different.

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