Question

The focal length of a ______ mirror is positive. *​

Answer 1

Answer:

convex mirror

Explanation:

According to cartesian system focal length of a concave mirror is negative whereas radius of curvature of convex mirror is positive.

(May it helps you)

Answer 2

The focal length of a convex mirror is positive.

Convex Mirror

• A convex mirror is a spherical mirror with the reflecting surface curved outwards. The image formed by a convex mirror is always virtual and diminished.

• The reason is focal length and the radius of curvature are imaginary points residing inside the mirror, and hence, unable to get reached them.

The focal length of the convex mirror

• the focal length (f) is the distance between the principal focus (F) and the pole (P) is the mirror. It is equivalent to half of the radius of curvature, that is, $f = 2R$ where R is the radius of curvature.
• The focal length of a convex mirror is always positive. This is because when the light rays, parallel to the principal axis, incident on a convex surface, it converges at the focus (on the inward surface) of the mirror, called the real focus.

The convex mirror has an outward reflecting surface. Due to this, the light ray travelling parallel to the principal axis meets at the real focus of the mirror. Therefore, the focal length is always positive.