Physics
JAMB 1979
The bulb of a motorcycle head-lamp is marked 40W, 6V. The resistance of the filament when it is switched on is
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A.
\(\frac{6^2}{40^2}\)ohms
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B.
\(\frac{40}{6^2}\)ohms
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C.
\(\frac{40}{6}\)ohms
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D.
6 x 40 ohms
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E.
\(\frac{6^2}{40}\)ohms
Correct Answer: Option E
Explanation
Power \(\frac{V^2}{R}\)
40 = \(\frac{6 \times 6}{r}\)
R = \(\frac{36}{40}\)\(\Omega\)
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