Write the expression for the power of a lens in terms of powers of its refracting surfaces.

Explanation

We know that `(1)/(f)=(n-1)((1)/(r_(1))-(1)/(r_(2)))`
i.e., `(1)/(f)=(n-1)/(r_(1))-(n-1)/(r_(2))`
`P=P_(1)+P_(2)`
where `P_(1)=(n-1)/(r_(1))`,
and `P_(2)= (n-1)/(-r_(2))`,
and `P=(1)/(f)`