Question

Is the power of a concave mirror positive or negative?

Answer 1

Concave mirror

1. A concave mirror is a spherical mirror with a dented inward reflecting surface. Incoming light beams are reflected and focused (parallel) to a point called the focus point by concave mirrors.
2. The power of the concave lens is negative. Concave lens surfaces have a virtual radius of curvature, and thus a negative curvature.
3. The focal length of a concave mirror is negative.
   

Power of concave mirror

1. The power of a lens is defined as reciprocal to focal length. For concave lenses, the power is negative because the focal length is negative. $p=\frac{1}{f}[p=power,f=focallength]$
2. We know that a concave lens diverges the rays incident on it. That’s why it is also known as a diverging lens. Hence, its power is negative.

Hence, the power of the concave mirror is negative.