### 6. Voltage and current

We have mentioned these terms a few times already, without having them explained properly.

Imagine a ball being thrown through the air.

• Voltage is the speed the ball is travelling. This is measured in Volts. It's symbol is a capital V.
• Current is the size of the ball being thrown. This is measured in Amperes (or Amps for short). Its symbol is a capital A.

All DC electricity can be thought of as having a voltage and a current. In order to determine what these are, you can use a multimeter.

##### Measure the voltage of a battery

Place the red probe on the positive terminal of the battery. Place the black probe on ground (or "minus") terminal of the battery. You should get a reading close to its nominal value, e.g. 9V.

If you reverse the probes of the multimeter you will notice that the meter will give you a negative voltage reading. The reason for this is that DC electricity has a positive voltage and a ground voltage. The reading on the multimeter is actually the black probe's voltage level subtracted from the level of the red probe.