“**Power of lens is a measure of the convergence or divergence, which a lens introduces in the light falling on it**.”

**It is defined as the tangent of the angle by which it converges or diverges a beam of light falling at unit distant from the optical centre. **

**Thus, Power of a lens is the reciprocal of focal length.**

When focal length is measured in metre then power is taken in __dioptre (D).__

**For converging lens**,, therefore P=+ve

**For diverging lens,** , therefore P =– ve.