A converging lens produces an image four times as large as an object placed 25cm...
PHYSICS
WAEC 2003
A converging lens produces an image four times as large as an object placed 25cm from the lens. Calculate its focal length
- A. 100cm
- B. 33cm
- C. 29cm
- D. 20cm
Correct Answer: D. 20cm
Explanation
M = \(\frac{v}{u}\)
v = mu = 4 x 25 = 100m
\(\frac{1}{v} + \frac{1}{u} = \frac{1}{f}\)
\(\frac{1}{100} + \frac{1}{25} = \frac{1}{f}\)
f = 20cm
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