Electromagnetic Devices

• What is an electromagnet?

  A solenoid containing an iron core
• Why are electromagnets used in appliances?

  They can be turned on and off safely
• What are the two appliances that use electromagnets?

  • Relay
  • Electric doorbell
• What does a relay contain?

  Two separate circuits
• What is the role of the low-voltage circuit in a relay?

  It contains an electromagnet that is safe
• What happens when the low-voltage circuit is turned on in a relay?


  A magnetic field is produced around the electromagnet
• How does the magnetic field affect the contacts in a relay?

  It attracts the iron block, closing the contacts
• What happens when the low-voltage circuit is switched off in a relay?

  The contacts spring apart, turning off the high-voltage circuit
• What is the function of the switch in an electric doorbell?

  It closes the circuit when pressed
• What occurs when the switch in a doorbell is closed?

  A current flows through the circuit
• What does the electromagnet do in a doorbell?

  It produces a magnetic field to attract the iron contact
• What happens to the iron contact when it is attracted by the magnetic field in a doorbell?

  It moves towards the magnetic field, hitting the bell
• What occurs after the clapper hits the bell in a doorbell?

  The circuit is broken, stopping the current flow
• What happens when the circuit is complete again in a doorbell?

  A current flows, repeating the process
• What should students remember about electromagnetic devices for their exam?

  • Understand how relays work
  • Know the function of electric doorbells
  • Be familiar with safety concerns in high-voltage circuits
• What is a relay?

   An electrically operated switch that uses an electromagnet to control a circuit, allowing a low-power signal to switch a higher-power one.