The power of a lens is a measure of the degree of convergence or divergence of light rays falling on it.

The power of a lens is defined as the reciprocal of its focal length in meters.

Power of lens=1focal length of lens(m)

P=1f(meters)

P=100 f(cm)

**Note:-**

- Unit of power of lens in
**Dioptre(D)** - The power of concave lens is negative(-ve)
- The power of convex lens is positive(+ve)
- A thick lens has short focal length but more power. A thin lens has large focal length but less power.

## Power of a combination of lenses:

If a number of lenses are placed in close contact, then the power of the combination of lenses is equal to the algebraic sum of the powers of individual lenses.

P=p1+p2

**Example:**Suppose convex lens has power +4D and concave lens of power -10D,So resultant power should be (4+(-10)=-6D) 6D. So this combination look like.

P= +4+(-10)

= +4-10

= -6 D

Power of a combination of lens |