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Laws of Reflection

For a telesco...

Question

For a telescope, the focal lengths of two lenses are 30 cm and 10 cm. One acts as objective and the other as eye-piece. The length of the telescope is

A

40 cm

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B

3 cm

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C

200 cm

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D

30 cm

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Solution

The correct option is A 40 cm
focal length of objective lens

$f_{o} = 30 c m$

focal length of eyepiece lens

$f_{e} = 10 c m$
The length of lens

$L = f_{o} + f_{e}$

$L = 30 + 10 = 40 c m$

Option A is correct.

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