Electric power dissipated by a conductor is defined as the amount of thermal energy that passes through it over a period of time.

The unit used for power is the watt **(W)**, which designates joule per second (J / s)

Considering that all energy lost in a circuit is the result of the Joule effect, we assume that energy transformed into heat equals energy lost by a charge. **what** passing through the driver. That is:

But we know that:

So:

Soon:

But we know that , so we can write that:

For example:

What is the current going through a 60W light bulb in a city where the voltage in the mains is 220V?

By Ohm's 1st Law we have to Then we can define two ways that relate electrical power to resistance.

So using the previous example, what is the resistance of the internal filament of the lamp?