Suitable For
Grade 8
Difficulty
3
Time Required
<2 Days
Supervision
Required
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?
- INSULATED COPPER WIRE
- 2x 9-VOLT BATTERIES
- 2x 9-VOLT LED’S
- SINGLE THROW SWITCH
- DOUBLE THROW RELAY
- WIRE CUTTERS
- ADULT HELPER
Procedure (Method)
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:
- Assemble the ‘first circuit’ (red) as per the diagram above by connecting a 9-Volt battery to a switch and a relay in series with insulated copper wires and alligator clips.
- Assemble the ‘second circuit’ (blue) as per the diagram above by now connecting two LED’s to the relay in series with another battery in between them connected to the relay in parallel.
- Turn on the switch (red circuit) and notice which of the LED’s lights up. When the switch is turned off, the other LED will light up!
How does it work?
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.
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