The premier destination for fun science projects & experiments for kids grades K-8 since 2010!


Build a relay to remotely control other electrical circuits

Suitable For

Grade 8



Time Required

 <2 Days



What’s it about?

An electrical relay is a switch which is under the control of another circuit. A classic relay consists of an electromagnet, used to control switches that may either ‘open’ or ‘close’ another electrical circuit. There are many reasons for using a relay, but mostly in situations where a small current flow is used to switch on a large current flow, or high voltage which also makes the system safer to use.

A classic example of an electrical relay is the system used to start a car. When someone turns an ignition key, the ignition does not interact directly with the car battery. Instead, it activates an electrical relay which passes the signal on so that the car can start. In this science experiment, use a ‘relay’ to control the activation of two LED’s by opening or closing a circuit to control another:

Topics covered

Electrical current, In Series, In Parallel, Relay, LED

What will I need?

  • 2x 9-VOLT LED’S

Procedure (Method)

Unfortunately, this section is only available in the e-book version of the project.

How does it work?

Unfortunately, this section is only available in the e-book version of the project.

The power or ‘electrical energy’ stored in a battery can only be released and allowed to flow when a complete circuit is made out of wires or other ‘conductors’ that conduct electricity. In this science experiment two separate power sources (batteries) are required to power specific items in two separate circuits. The one battery (red circuit) delivers power to the ‘relay coil’ when the switch is turned on, while the other battery is used to light the LED’s. It depends on whether the relay’s coil or ‘electromagnet’ is switched on or not that lights up a specific LED in the ‘blue circuit’. The one LED would be lit when the switch in the relay coil circuit is off, and the other LED will be lit when the switch is on.

Like the sound of it?

Why not check out the full worksheet in one of our popular e-books?

This particular science project can be found in any of the following Experiland e-books:

Experiland e-books contain detailed steps, including illustrations, to complete the science projects from start to finish.

Science project ebooks for kids

Experiland's science e-books contain a diverse range of several hundred of exciting science projects, ideas and experiments.

A project introduction and background, complete listing of required materials, step-by-step instructions on how to carry out the project, why it works, learn more section, as well as a science glossary with all the relevant terms make up each of the all-inclusive science project worksheets in our e-books!

Get your e-Book!