Question

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

Answer 1

Answer: The correct answer is 22.15 ohm.

Explanation:

The expression for the power in terms of resistance and potential is as follows;

$P=\frac{V^{2} }{R}$

Here, V is the potential, P is the power and R is the resistance.

It is given in the problem that an electric device uses 650 watts of power. The voltage of this device is 120 V.

Calculate the resistance of the electric device by rearranging the above expression.

$R=\frac{V^{2} }{P}$

Put V= 120 V and P= 650 W.

$R=\frac{(120)^{2} }{650}$

$R=22.15 ohm$

Therefore, the value of the resistance is 22.15 ohm.

Answer 2

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  .