For a combination of lenses, the power of each lens is added to get the resultant power.
P = P1 + P2. WHY?

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Solution

Power of combination of lenses : The focal length of the combination of two lenses placed in contact is given by the relation.

1/F = 1/f1 +1/f2

If p1 is the power of lens of focal length f1, p2 the power of the focal length f2 and P the power of the combination of focal length, F then,

P = p1 +p2

Thus the power of combination of lenses is the algebraic sum of the powers of individual lenses.

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Similar questions

Q. If the power of two lenses and

P_{1}

and

P_{2}

; when they are combined; the effective power is:

(a) What do you understand by the power of a lens? Name one factor on which the power of a lens depends.

(b) What is the unit of power of a lens? Define the unit of power of a lens.

(c) A combination of lenses for a camera contains two converging lenses of focal lengths 20 cm and 40 cm and a diverging lens of focal length 50 cm. Find the power and focal length of the combination.

Q. Assertion :If a convex lens of focal length 40 cm is put in contact with a concave lens of 25 cm, then the power of the combination is -

1.5 D

. Reason:

P = P_{1} + P_{2} = \frac{1}{f_{1}} + \frac{1}{f_{2}}

Q. The resultant power of combination of lenses.

Q. Assertion :If

P_{1}

and

P_{2}

be the powers of two thin lenses located coaxially in a medium of refractive index

μ

at a distance d, then the power P of the combination is

P = P_{1} + P_{2} - \frac{P_{1} P_{2} d}{μ}

Reason: Because for above given system equivalent focal length is given by

F = \frac{f_{1} f_{2}}{f_{1} + f_{2} - d / μ}

and

P = \frac{1}{F} .

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For a combination of lenses, the power of each lens is added to get the resultant power. P = P1 + P2. WHY?

For a combination of lenses, the power of each lens is added to get the resultant power.
P = P1 + P2. WHY?