The electric power, expressed in watts, is the rate at which electric energy is converted into another form of energy such as light or heat.
1 watt is the consumption of 1 joule of energy every second.
1000 watts = 1000 joules every second
40 J/s, 1500 J/s, and 7200 J/s are all examples of electric powers.
The electric power is also the product of current and voltage.
Electric power = current × voltage
1 watt = 1 ampere × 1 volt
At this point, you may not quite see why we are multiplying the current and the voltage to get the power. A little math will clarify this!
Recall that in the lesson about electric current, we saw that 1 ampere = 1 coulomb of charge per second.
The word per means divided by. Therefore, we can rewrite 1 coulomb of charge per second as shown below.
Recall also that in the lesson about electric potential, we saw that 1 volt = 1 joule of energy per 1 coulomb of charge.
Therefore, we can rewrite 1 joule of energy per 1 coulomb of charge as shown below.
We can multiply a current of 1 ampere by a voltage of 1 volt to see what we end up with.
current × voltage =
1 coulomb
1 second

×
1 joule
1 coulomb

current × voltage =
1 coulomb
1 second

×
1 joule
1 coulomb

1 coulomb gets cancelled since it is on top and at the bottom.
In the lesson about power, we saw that 1 joule of energy per second = 1 watt and watt is a unit of power.
From the formula, you can see that the electric power is the rate at
which energy is transferred. This second definition of electric power
can also help us to calculate the cost of electric energy and we will
show you how in a different lesson.