# Electrical Power

### From DT Online

##### Description

**Power** is *‘the rate of doing work’* - i.e. the same work is done lifting a weight quickly or slowly but more power is needed to do it quickly.

**Work** is measured in **joules** and the SI unit of power is the watt, or one joule per second - the **International System of Units (SI)** is the modern form of the metric system.

For electrical power a watt * (W)* is equal to one unit of electrical current, amp

*, multiplied by one volt*

**(A)***.*

**(V)****Note:**
all three * units are named after people* which is why capital letters are used for the letter symbol - but not for the unit name itself.

##### Features and Applications

If the three symbols for watt * (W)*, current

*and voltage*

**(I)***are arranged in a triangle as shown, then the various relationships can easily be seen - the symbol*

**(V)***is used to represent the current which is measured in amps*

**(I)***(see below)*

- Watts = Volts x Current
**(W = V x I)** - Volts = Watts / Current
**(V = W / I)** - Current = Watts / Volts
**(I = W / V)**

A similar triangular graphic may be used to show the various **Ohm's Law** relationships between electrical voltage * (V*), current

*and resistance*

**(I)***.*

**(R)**Through these Ohm's Law relationships, it can be seen that * V = I x R* so if

*is substituted above then Watts can also be derived as current squared multiplied by resistance*

**V**

**(W=I**^{2}xR)**Note:**
Abbreviations are usually named after the thing you're measuring, not the unit. So resistance is R, not O for ohms (Ω) but voltage is measured in volts, so it's V either way *(the term ' electromotive force and the symbol E are becoming less common, replaced by voltage and V)*