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Question
Define electric power. An electrical device of resistance R is connected across a source of voltage V and draws a current I. Derive an expression for power in terms of current and resistance.
Solution
Electric power is defined as the rate of consumption of energy or simply the rate of doing work.
i.e., power, P =`(" work done"("W"))/("Time"("t"))` ..............(i)
The work done by current (I) when it flows in a potential (V) for time (t) can be given by
W = VIt …………………. (ii)
⇒ Power, P `= "VIt"/"t"="VI"`
∴Electric power, P = VI
From Ohm's law, V=VI
Thus, electric power is given by, P = (IR)I = I2R
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