Question

The focal length F of a lens made by combining two lenses of focal length U and V is given I/F=I/U+I/V

A.make V the subject of the formula.
B.find V when F=6,U=10
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Answer 1

a).
`V=(U.F)/(U-F)`

b). V = 15 units

Explanation:

Focal length F of a lens made by combining two lenses of different focal lengths U and V will be,

`(1)/(F)=(1)/(U)+(1)/(V)`

A). By solving the given formula,

`(1)/(V)=(1)/(F)-(1)/(U)`

`(1)/(V)=(U-F)/(U.F)`

`V=(U.F)/(U-F)`

B). If F = 6 and U = 10 then we have to find the value of V.

By substituting the given values in the formula,

`V=(6* 10)/(10-6)`

`V=(60)/(4)`

V = 15 units

Therefore, focal length (V) of the lens = 15 units