Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!

Home > Science > Energy, electricity and forces > Electric current and voltage

Science

Electric current and voltage

Print

Measuring amps & volts

You need to know how to measure current and voltage.

Current

Current is a measure of how much electric charge flows through a circuit. The more charge that flows, the bigger the current.

Current is measured in units called amps. The symbol for amps is A. For example, 20A is a bigger current than 5A.

Measuring current

A device called an ammeter is used to measure current. Some types of ammeter have a pointer on a dial, but most have a digital readout. To measure the current flowing through a component in a circuit, you must connect the ammeter in series with it.

Two circuits, both with a cell, an ammeter, and a lamp. In the first, the ammeter is connected before the lamp. In the second, the ammeter is connected after the lamp

Voltage

Voltage is a measure of the difference in electrical energy between two parts of a circuit. The bigger the difference in energy, the bigger the voltage.

Voltage is measured in volts. The symbol for volts is V. For example, 230V is a bigger voltage than 12V.

Measuring voltage

Voltage is meaured using a voltmeter. Some types of voltmeter have a pointer on a dial, but most have a digital readout. To measure the voltage across a component in a circuit, you must connect the voltmeter in parallel with it.

Shows a circuit with a cell, a lamp, and a voltmeter. The voltmeter is connected in parallel to the lamp

Using a voltmeter to measure the voltage across a lamp

You can measure the voltage across a cell or battery. The more cells, the bigger the voltage.

One circuit has a voltage of 1.5V. A lamp and a voltmeter are connected. The other circuit has a voltage of 4.5V. It has a lamp and a voltmeter connected

The more cells, the bigger the voltage

Checkpoint

  Current Voltage
Measured in amps, A volts, V
Measured with ammeter in series voltmeter in parallel
Circuit symbol of measuring devise A circle with an A in it A circle with a V in it

Activity

Electric current and voltage activity

Danger! Danger! High voltage! Whatever you do, don't click this link!

Play

Whack Attack

Whack and zap mad professors and aliens!

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.