The magnifying power of a telescope is 9 in normal adjustment. When it is adjusted for parallel rays, the distance between the objective lens and the eyepiece is 20cm. The focal length of the lenses are -
A
15cm,5cm
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B
10cm,10cm
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C
18cm,2cm
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D
11cm,9cm
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Solution
The correct option is C18cm,2cm Given: m=9 L=20cm
We know that, in normal adjustment, the final image is formed at infinity.