Power of Combination of Lenses
Power of Combination of Lenses
Power of Lens:
The power of a lens is defined as the reciprocal of its focal length.
Here SI unit for the focal length is meters. The S.I. unit of power is diopter(D).
Power of Combination of Lens:
When two or more thin lenses are kept in contact with each other such that they have the same principal axis, then the power of the combination is treated as a single thin lens.The power of this combination is equal to the algebraic sum of powers of individual lenses i.e.
.
When two or more thin lenses are used in combination, the equivalent focal length (f) can be calculated as the reciprocal of the resultant power of the combination (P). The focal length F of the equivalent single lens is given by:
Let us take the case of two lenses of focal length and
. The power of these lenses be
and
. Then
Which of the following are correct ? (a) When two or more thin lenses are used in combination, the equivalent focal length (f) can be calculated as the reciprocal of the resultant power of the combination (b) The S.I. unit of power is diopter (D). (c) The combination of lens is used in designing of camera lenses and the objectives of microscopes and telescopes. | |||
| Right Option : D | |||
| View Explanation | |||
The SI unit of power is ____________________ . | |||
| Right Option : C | |||
| View Explanation | |||
The SI unit for the focal length is ___________________ . | |||
| Right Option : A | |||
| View Explanation | |||
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