11.1.10

Relays

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Circuit Components: Relays

A relay is a switch that is operated by an electromagnet.

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How they work

  • When a small current passes through the electromagnet, the soft iron arm is attracted to the electromagnet. This arm pushes against a switch to close it.
  • When the current stops, the arm moves back and the switch opens again.
  • The switch in a relay can be normally open or normally closed.
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Using relays

  • In a relay, the circuit containing the switch is separate from the circuit containing the electromagnet.
  • The circuit with the electromagnet can have a small electric current. However, this circuit can switch a circuit with a dangerously high electric current on or off.
  • Relays can be used alongside light dependent resistors (LDRs) and thermistors to create environment sensitive switches.
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Making a light sensitive switch

  • A light dependent resistor (LDR) is connected in the same circuit as the electromagnet.
  • When light shines on the LDR, its resistance falls and the electric current through the electromagnet increases.
  • The increase in current turns the electromagnet on and activates the switch in the other circuit.
Illustrative background for Making a temperature dependent alarmIllustrative background for Making a temperature dependent alarm ?? "content

Making a temperature dependent alarm

  • A thermistor is connected in the same circuit as the electromagnet.
  • When the thermistor heats up, its resistance falls and the electric current through the electromagnet increases.
  • The increase in current turns the electromagnet, and the circuit containing the alarm on.

Jump to other topics

1Physical Quantities & Units

2Measurement Techniques

3Kinematics

4Dynamics

5Gravitational Fields

6Deformation of Solids

7Thermal Physics

8Oscillations

9Communication

10Electric Fields

11Current Electricity

12Magnetic Fields

13Modern Physics

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