Question
State the formula for electric power. Hence, obtain its SI unit.
✓
Answer
Electric power $(P)=$
electric work $(W)$ done or electric energy used
time $(t)$
The SI unit of work is the joule and that of time is the second. Hence, the SI unit of power is the joule per second. It is given the special name: the watt (W). One watt equals one joule per second.
$
\begin{aligned}
& W = VIt = I ^2 Rt =\frac{V^2}{R} t \\
& \therefore P = W / t = VI = I ^2 R = V ^2 / R .
\end{aligned}
$
Here, $V$ is the potential difference applied across an electrical appliance, $R$ is the resistance of the appliance and $I$ is the current through the appliance.
[ Note The SI unit of power, the watt, is named in honour of James Watt (1736-1819), British instrument maker and engineer. ]
electric work $(W)$ done or electric energy used
time $(t)$
The SI unit of work is the joule and that of time is the second. Hence, the SI unit of power is the joule per second. It is given the special name: the watt (W). One watt equals one joule per second.
$
\begin{aligned}
& W = VIt = I ^2 Rt =\frac{V^2}{R} t \\
& \therefore P = W / t = VI = I ^2 R = V ^2 / R .
\end{aligned}
$
Here, $V$ is the potential difference applied across an electrical appliance, $R$ is the resistance of the appliance and $I$ is the current through the appliance.
[ Note The SI unit of power, the watt, is named in honour of James Watt (1736-1819), British instrument maker and engineer. ]
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