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If the focal length of a camera lens is 20cm, the distance from the film at which the ...

If the focal length of a camera lens is 20cm, the distance from the film at which the lens must be set to produce a sharp image of an object 100cm away is
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  • A 17cm
  • B 20cm
  • C 25cm
  • D 100cm
Correct Answer: Option C
Explanation:
F = \(\frac{uv}{u + v}\)
20 = \(\frac{100 \times v}{100 + v}\)
v = 25cm

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