If the focal length of a camera is 20cm the dis... - JAMB Physics 2018 Question
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
A
17cm
B
20cm
C
25cm
D
100cm
correct option: a
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
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