Question

A torch bulb is rated 2.5 V and 750 mA. Calculate (i) its power (in W), (ii) its resistance (in $\Omega$) and (iii) the energy consumed (in J) if this bulb is lighted for four hours.

Answer 1

$\left(1\right)$ Power is given by $P=VI=2.5\times 0.75=1.875W$

$\left(2\right)$ Resistance is given by $R=\frac{V}{I}=\frac{2.5}{0.75}=3.33\Omega$

$\left(3\right)$ Time Given$=4hr=4\times 60\times 60sec$

$=14400sec$

Energy Consumed $E=Pt$

$=1.875\times 14400$

$=27000J$