Question

Why are images not always in focus on a concave mirror, even though light from a point source travels in different directions and some light rays are parallel to each other?

a. Concave mirrors have a single focal point, so all light rays converge to that point.

b. Light rays do not always reach the mirror surface at the correct angle.

c. The reflectivity of the mirror surface varies, causing different points of reflection.

d. Concave mirrors only work with collimated light sources.

Answer 1

Concave mirrors may not focus light properly if they are too large compared to their radius of curvature, causing reflected rays not to meet at a single point, leading to an undefined focal point. For a sharp focus, use a smaller concave mirror, which can approximate a well-defined focal point.

Step-by-step explanation:

Images in a concave mirror are not always in focus because the shape of the mirror and its relation to the radius of curvature affect the convergence of light rays. A large spherical mirror compared to its radius of curvature causes reflected rays to not intersect at the same point, resulting in a lack of a well-defined focal point. For a spherical concave mirror to have a well-defined focal point, it must be small compared to its radius of curvature, a principle similar to the thin lens approximation. Additionally, spherical mirrors have a positive focal length because they are converging mirrors, unlike convex mirrors which diverge light rays and have a negative focal length.