Sign of Focal Length of Concave Mirror
Concave mirrors are curved mirrors that reflect light inwards. The focal length of a concave mirror can be positive or negative, depending on the position of the focal point relative to the mirror.

Positive Focal Length
When the focal point of a concave mirror is on the same side as the incident light, the focal length is considered positive. This means that the light rays converge at the focal point after reflecting off the mirror. Positive focal lengths are common in concave mirrors used for magnification purposes, such as shaving mirrors or makeup mirrors.

Negative Focal Length
On the other hand, when the focal point of a concave mirror is on the opposite side of the incident light, the focal length is negative. This indicates that the light rays appear to diverge from the focal point after reflection. Negative focal lengths are typical for concave mirrors used in optical systems like telescopes or cameras.

Visual Representation
To visualize the sign of the focal length of a concave mirror, imagine the light rays parallel to the principal axis. If they converge after reflection, the focal length is positive. If they appear to diverge, the focal length is negative.
In conclusion, the sign of the focal length of a concave mirror is determined by the position of the focal point relative to the mirror. Positive focal lengths indicate converging light rays, while negative focal lengths signify diverging light rays.