Question

An alarm clock is plugged into a 120 volt outlet and has a resistance of 15,000 ohms. How much power does it use?

Answer 1

The power used is 0.96 watts.

Step-by-step explanation:

Recall the formula for electric power (P) as the product of the voltage applied times the circulating current:

`P=V\,\,I`

and recall as well that the circulating current can be obtained via Ohm's Law as the quotient of the voltage applied divided the resistance:

`V=I\,\,R\\I=(V)/(R)`

Then we can re-write the power expression as:

`P=V\,\,I=V\,\,(V)/(R) =(V^2)/(R)`

which in our case becomes:

`P=(V^2)/(R)=(120^2)/(15000) =0.96\,\,watts`