# Electrical power

Electrical power is the rate or speed at which electrical energy is transferred in a circuit. It can also be thought of as the rate at which energy is consumed by an item in an electrical circuit. The formula for calculating electrical power is:

Electrical power turned me into the village idiot.

**NOTE:**

Electrical power is measured in watts. One watt of electrical power is one joule per second.

**Example 1**

A lamp is rated at 12V, 6W. How many joules of energy are transferred by the lamp in 5 minutes? And what is the current passing through the lamp when it is connected to a 12V supply?

**Answer**

6 watts = 6 joules per second

5 minutes = 60 x 5 = 300 seconds

So the energy transferred = 300 x 6 = 1800 Joules

Power = voltage x current P = VI

Divide both sides by voltage to make current the subject,

\frac{Power}{voltage}=\frac{\strike{voltage}\times current}{\strike{voltage}}

So current I = P/V 6/12 = 0.5 Amps

**Example 2**

The circuit below shows where an ammeter and voltmeter are placed. If the ammeter reads 2A and the voltmeter reads 6V, what is the power of the lamp?

**Answer**

Power = voltage x current P = VI

Power = 6 x 2 = 12 watts.