Power Of Lens And Mirror MCQ - Practice Questions with Answers

Power and lens and mirror-

Power of a lens is defined as the reciprocal of focal length and Power of a mirror is defined as the negative of reciprocal of focal length.

So,

$$
P_{\text {Lens }}=\frac{1}{f} \quad \text { and } \quad P_{\text {Mirror }}=\frac{-1}{f}
$$

Where, $f=$ focal length
The unit of power is Diopter, $1 \mathrm{D}=\mathbf{1} \mathbf{~ m}^{-1}$
The sign of the focal length will be taken according to the sign convention which we have discussed in the previous concept.

The power of a combination of lenses in contact is the algebraic sum of the powers of individual lenses, so it can be written as -

$$
P_{\text {Total }}=P_I+P_2+P_3+\cdots+P_n
$$