# How much power is produced if a voltage of 4V

How much power is produced if a voltage of 4V is applied to a circuit with a resistance of $27\mathrm{\Omega }$ ?
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Lucille Lucas
Probably not a lot more explanation needed. We are given a voltage (V) And a resistance ($\mathrm{\Omega }$). We know that the expression for power in a circuit is P=VI, but we don't know the current.
We do know a way to find the current, given the voltage and the resistance: Ohm's Law :
V=IR
Rearranging:
$I=\frac{V}{R}$
We could calculate the current and then substitute that into the expression for the power, but I decided to combine the equations instead:
$P=VI=V\left(\frac{V}{R}\right)=\frac{{V}^{2}}{R}$
Then it's just a matter of substituting in the values we have and we know the power produced by the circuit.