Power Rating

Power Rating

1. Figure above is an example of power rating label.
2. An electrical appliance which is marked 240V, 1200W means that the electrical appliance will consume 1200J of energy in every second if the potential difference across it is 240V.

Example
A bulb rated 240V/80W is operated from a 120V power source. Find the resistance and the current flows through it.

Answer:
$$\begin{array}{l}P=\frac{V^2}{R}\\ 80=\frac{{\left(240\right)}^2}{R}\\ R=\frac{{\left(240\right)}^2}{80}=720\Omega \end{array}$$
The current flows through the bulb
$$\begin{array}{l}I=\frac{V}{R}\\ I=\frac{120}{720}=0.167A\end{array}$$