A concave mirror has a radius of curvature of 40\text{ cm}. What is the focal length of th… — JAMB UTME

A concave mirror has a radius of curvature of $40\text{ cm}$ . What is the focal length of the mirror?

The focal length of the concave mirror is

20\text{ cm}

For any spherical mirror, the focal length is half of its radius of curvature (

f = \frac{r}{2}

). Since the mirror is concave, its focal length is positive, yielding

\frac{40\text{ cm}}{2} = 20\text{ cm}

Identify the given physical quantity

Radius of curvature

r = 40\text{ cm}

for a concave mirror.

The radius of curvature is the distance from the pole to the center of curvature.

Apply the relationship between focal length and radius of curvature

f = \frac{r}{2} = \frac{40\text{ cm}}{2} = 20\text{ cm}

For spherical mirrors, the principal focus lies halfway between the pole and the center of curvature.

Focal length of spherical mirrors

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