Question

(a) Define (i) principal focus of a concave mirror, and (ii) focal length of a concave mirror. Draw a diagram to represent the action of a concave mirror on a beam of parallel light rays. Mark on this diagram principal axis, focus $F$ , center of curvature $C$ , pole $P$ and focal length $f$ of the concave mirror.

Answer 1

A concave mirror is a mirror that has a reflecting surface curved inside from the middle. A concave mirror is a mirror that is silvered from the inside of the sphere. It reflects the light at the same angle as it receives from the object.

Complete Step by Step Answer:
i. PRINCIPAL FOCUS: The principal focus of a concave mirror is a point on the principal axis of a mirror at which all the light rays parallel rays converge after reflecting from the mirror.

ii. FOCAL LENGTH: The focal length of a concave mirror is defined as the distance between the pole and the focus of the mirror and is calculated by using the following formula
$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$

Here, $f$ represents the focal length, $v$ is the distance of the image from the mirror, and
$u$ is the distance of the object from the mirror.

The diagram that represents the action of a concave mirror on a beam of parallel light rays is given below

Here, $F$ represents the focus and $P$ represents the pole and $C$ represents the radius of
curvature of the concave mirror. Here, the rays that are parallel to the principal axis intersect at the focus after reflecting from the mirror.

Note: The principal axis of a concave mirror is the line through the center of the surface and the center of curvature of all the segments of a mirror. The center of curvature of a concave mirror is the point from which the mirror is cut. The center of curvature of a concave mirror is equal to the radius of curvature.