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Power of lens and mirror is considered one of the most asked concept.
19 Questions around this concept.
Direction: In the following question, a statement of Assertion (A) is followed by a statement of reason (R). Mark the correct choice as:
Assertion: The power of a convex lens is positive and that of a concave lens is negative.
Reason: The power of lens is P =$\frac{1}{f}$
A biconcave lens of power P vertically splits into two identical plano concave parts. The power of each part will be
A biconvex lens of focal length f is cut into two identical plano convex lenses. The focal length of each part will be
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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,
So,
$
P_{\text {Lens }}=\frac{1}{f} \quad \text { and } \quad P_{\text {Mirror }}=\frac{-1}{f}
$
Where, $\mathrm{f}=$ 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
$
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