The radius of curvature of a spherical mirror is 20 cm . Find its focal length.

Given, The radius of curvature, R = 20 cm Let f be the focal length of the spherical mirror. The radius of curvature of a spherical mirror = 2 × Focal length R = 2 f Hence, f = R 2 ⇒ f = 20 cm 2 = 10 cm Thus, the focal length of the given spherical mirror is 10 cm .

Define the radius of curvature of the spherical mirror.

The centre of curvature of a spherical mirror is the centre of the hollow sphere of glass of which the spherical mirror is a part. The distance between the centre of curvature and the pole is known as the radius of curvature. In other words, we can say that, the radius of curvature is the radius of the hollow sphere of glass of which mirror is a part. The radius of curvature is denoted by the letter ‘ R ’ .

Find the power of a concave lens of focal length 2 m .

The power of a lens is a measure of the degree of convergence or divergence of light rays falling on it. A type of lens that diverges a straight light beam from the source to form a diminished, upright, virtual image is known as a concave lens. According to the sign convention, the focal length of a concave lens is always negative. Given, The focal length of the lens, f = - 2 m We know that, Power = 1 Focal lenth of the lens ( in metres ) P = 1 f ⇒ P = 1 ( - 2 m ) = - 0 . 5 D Thus, the power of the concave lens is - 0 . 5 D .

Define the power of lens.

The power of a lens is a measure of the degree of convergence or divergence of light rays falling on it. We can also define the power of the lens as the reciprocal of its focal length in metres. Power = 1 Focal length of the lens ( in metres ) P = 1 f For a concave lens, the focal length is negative and so power is negative. For the convex lens, the focal length is positive and so, the power is positive.