Question

How much power is produced if a voltage of `4 V` is applied to a circuit with a resistance of `27 Omega`?

Answer 1

Combining `P=VI` and `V=IR` (Ohm's Law) yields `P=V^2/R = 4^2/27 = 16/27 ~~0.59` `W`

Explanation:

Probably not a lot more explanation needed. We are given a voltage `(V)` and a resistance `(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=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(V/R)=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.