If the object distance and the image distance from a concave mirror is -20 cm, what is the focal length of the mirror?

Explanation

CONCEPT: Mirror A mirror is a polished surface that reflects the light incident on it. Types of the mirror: 1. Plane mirror 2. Spherical mirror Concave mirror Convex mirror Mirror Formula: Where u = distance of the object from the mirror, v = distance of the image from the mirror, and f = focal length Calculation: Given u = -20 cm, and v = -20 cm According to the mirror formula, -----(1) By equation 1, ⇒ ​ = f 1 ​ + u 1 ​v 1 ⇒ ​ = f 1 ​ + u 1 ​v 1 ⇒ ​ = f 1 ​ + −20 1 ​ −20 1 ⇒ ​ = f 1 − ​ 10 1 ⇒ f = - 10 cm The negative sign shows that the focus point lies on the same side of the mirror , from where the incident ray is coming.