Question

A typical incandescent bulb has an efficiency of about 10%. What current is needed for a bulb with a resistance of 1.5×10^2 Ω to output power of 6.0 W?

Answer 1

Explanations & Calculations

• Working power of the bulb

$\qquad\qquad \begin{aligned} \small P&=\small 6.0\,W\times\frac{100}{10}=60.0\,W \end{aligned}$

• The the current consumed at that power would be

$\qquad\qquad \begin{aligned} \small P&=\small I^2R\\ \small I &=\small \sqrt{\frac{60.0\,W}{1.5\times10^2\, \Omega}}= 6.3\times10^{-1}\,A \end{aligned}$