If the focal length of a camera is 20cm, the distance from the film at which the lens must be set to produce a sharp image of 100cm away is
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Correct Answer: Option A
Explanation:
F = 20cm
 V = 100cm
 U = ?
 \(\frac{1}{U}\) + \(\frac{1}{V}\) = \(\frac{1}{F}\)
\(\frac{1}{20}\) + \(\frac{1}{100}\) = \(\frac{1}{F}\)
 5 + \(\frac{1}{100}\) = \(\frac{1}{F}\)
 F = \(\frac{100}{6}\)
 = 16.7cm
 = 17cm
F = 20cm
 V = 100cm
 U = ?
 \(\frac{1}{U}\) + \(\frac{1}{V}\) = \(\frac{1}{F}\)
\(\frac{1}{20}\) + \(\frac{1}{100}\) = \(\frac{1}{F}\)
 5 + \(\frac{1}{100}\) = \(\frac{1}{F}\)
 F = \(\frac{100}{6}\)
 = 16.7cm
 = 17cm