# AC and DC

Variable | Symbol | Unit | Definition |
---|---|---|---|

Charge | Coulomb ( |
||

Current | Ampere ( |
||

Potential Difference | Volt ( |
||

Energy | Joule ( |
||

Power | Watt ( |
||

Resistance | Ohm ( |

### Direct Current

**Direct current**, or **DC**, is a type of current in which electrons all flow **in the same direction**. It does not have to be a constant voltage - any **absolute function** can be a DC function. In other words, it **never dips below the X axis** of a voltage-time graph.

### Alternating Current

**Alternating current**, or **AC**, is a type of current in which the direction the electrons are flowing in **rapidly changes**.

#### Peak Voltage

The peak voltage is the **maximum** instantaneous voltage reached by an AC waveform. It can be thought of as the **amplitude** of the wave, assuming the wave is centred at the X axis without any deflection.

#### RMS Voltage

The RMS voltage of a sinusoidal AC waveform is the **DC equivalent** which gives the **same amount of average power**. It is always **less than the peak voltage**.

While it may be tempting to think of this as the average absolute voltage, or even just the average voltage, it is **not** the same!

#### Formula

is the peak voltage, in volts. is the RMS voltage, in volts.