Question

Calculate the focal length of a convex mirror of radius of curvature 20cm.
(A) 5 cm
(B) 10cm
(C 15cm
(D) 20cm

Answer 1

The focal length of a convex mirror is the half of the radius of curvature. The focal length and radius of curvature of a convex mirror is positive. A convex mirror is an example of a diverging mirror and is a curved mirror in which the reflective surface bulges towards the light source Convex mirrors generally are not used to focus light since they reflect light outwards.
Formula used:
$f=\dfrac{R}{2}$
where, f is the focal length
R is the radius of curvature

Complete answer:
$f=\dfrac{R}{2}$
where, f is the focal length
R is the radius of curvature
Given that R=20cm
Thus, $f=\dfrac{20}{2}$
$\therefore f=10cm$

Hence option (B) is correct.

Additional information:
A convex mirror is an example of a diverging mirror and is a curved mirror in which the reflective surface bulges towards the light source. Convex mirrors generally are not used to focus light since they reflect light outwards. Virtual images are always formed by convex mirrors. Plane mirrors and convex mirrors will always produce an upright image if the object is located in front of the focal point. The focal length of a convex mirror is the half of the radius of curvature. The focal length and radius of curvature of a convex mirror is positive.

Note:
Convex mirrors generally are not used to focus light since they reflect light outwards. The image is usually smaller than the object, but gets larger when the object is near the mirror. Virtual images are always formed by convex mirrors. Plane mirrors and convex mirrors will always produce an upright image if the object is located in front of the focal point.