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Power Of Lens And Mirror - Practice Questions & MCQ
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main
Quick Facts
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Power of lens and mirror is considered one of the most asked concept.
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12 Questions around this concept.
Solve by difficulty
A person has been using spectacles of power $−1.0$ dioptre for distant vision and a separate reading glass of power $2.0$ dioptres. What is the least distance of distinct vision for this person :
A convex lens and a concave lens, each having the same focal length of are put in contact to form a combination of lenses. The power in diopters of the combination is:
Two lenses are placed in contact with each other and the focal length of the combination is . If the focal length of one is
, then the power of the other will be:
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An achromatic convergent doublet of two lenses in contact has a power of . The convex lens has power
. What is the ratio of the dispersive powers of the convergent and divergent lenses?
The nearer point of the hypermetropic eye is . The lens to be used for its correction should have the power:
Concepts Covered - 1
Power of lens and mirror
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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