# The focal length of a spherical mirror of radius of curvature 30 cm is:**(a) **10 cm **(b) **15 cm **(c) **20 cm **(d)** 30 cm

**(b) 15 cm**

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__Explanation__

Given,

Radius of curvature = $r$ = 30 cm

To find = $f$ = Focal length

__Solution__

We know that the focal length of a spherical mirror is half of its radius of curvature.

Mathematically it is given as-

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

Now, putting the given value we get-

**$f=\frac{1}{2}\times 30$**

$f=15cm$

Hence, the focal length of the spherical mirror will be **15c**m.

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