What is meant by the power of a lens ? What is its S.I. unit? Name the type of lens whose power is positive. The image of an object formed by a lens is real, inverted and of the same size as the object. If the image is at a distance of 40 cm from the lens, what is the nature and power of the lens? Draw ray diagram to justify your answer.

Power of a lens is the ability of the lens to converge or diverge the light falling on it. Mathematically, it is expressed as the reciprocal of the focal length of the lens.

Power of a lens,

P = lf (in m)

The S.I unit of power is dioptre (D).

1 D = 11 m

The power of a convex lens is positive.

It is given that the image of the object formed by the lens is real, inverted and of the same size as the object. Also, we know that only convex lens can form a real and inverted

The image, the given lens is aconvex lens. Inthe given case the object is placed at 2F1 and the the image is formed at 2F2