An electric device uses 650 watts of power. If the voltage is 120 volts, what is the resistance?

A. 78,000 ohms

B. 22 ohms

C. 0.18 ohms

D. 3,500 ohms

There are several handy-dandy formulas for electrical power.

Here they are:

- - Power = (voltage) x (current)

- - Power = (current²) x (resistance)

- - Power = (voltage²) x (resistance)

We just have to pick the one that's most convenient.

We know the power and the voltage, and we have to find the resistance.

So we would be smart to use a formula that has power, voltage, and

resistance in it. The last formula on my list is exactly what we want.

- - Power = (voltage²) / (resistance)

650 w = (120 v) ² / (resistance)

(650 w) x (resistance) = (120 v) ²

resistance = (120 v) ² / (650 w) = 22.2 ohms.