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# What is the relation between the focal length and radius of curvature of a spherical mirror (concave mirror or convex mirror)? Calculate the focal length of a spherical mirror whose radius of curvature is 25 cm.

For a spherical mirror (concave mirror or convex mirror), the principal focus $(F)$ lies exactly midway between the pole $(P)$ and centre of curvature $(C)$.

So, the focal length $(f)$ of a spherical mirror is equal to half of its radius of curvature $(R)$.

Mathematically it is given as:

**$f=\frac{1}{2}R\ or\ R=2f$**

Radius of curvature = $R$ = 25 cm (given)

Focal length $f$ = ?

We know that

$f=\frac{1}{2}R\$

Putting the given value in the equation we get-

$f=\frac{1}{2}\times 25$

$f =12.5cm$

Hence, the focal length of a spherical mirror will be **12.5cm.**

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