Back to: Fundamentals

### what is power?

Power in physics can relate to more than one category, it is used in both mechanics and electronics. However, whether we are talking about electric power or mechanical power, it still means the same thing – **the rate at which work is done**. In electronics, it is specifically **the rate per unit of time, at which electrical energy is transferred by an electric circuit**.

### unit

The unit of power is the **watt **and the symbol is **W**. This is named after an 18th-century Scottish inventor – James Watt.

### calculating power

power is calculated by the formula **V x I**

#### example

```
Imagine a heater that is powered from 230V and a current of 4A passes through it.
The power will be:
P = V x I
= 230 x 4
=
```**920W**

If we know the voltage and the resistance of the heater, we can calculate the power with an alternative formula, **P = V ^{2} / R**

#### example

```
Imagine a heater that is powered from 230V and has a resistance of 57.5Ω passes through it.
The power will be:
P = V
```^{2}/R
= 230^{2} / 57.5
= 52900 / 57.5
= **920W**

If we know the current and the resistance of the heater, we can calculate the power with an alternative formula, **P = I ^{2} x R**

#### example

```
Imagine a heater that is powered from 230V and has a resistance of 57.5Ω.
The power will be:
P = I
```^{2} x R
= 4^{2} x 57.5
= 16 x 57.5
= **920W**