The bulb of a motorcycle head-lamp is marked 40W, 6V. The resistance of the filament when it is switched on is
-
A.
(frac{6^2}{40^2})ohms -
B.
(frac{40}{6^2})ohms -
C.
(frac{40}{6})ohms -
D.
6 x 40 ohms -
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)