Electromagnetism

• What happens when a current flows through a wire?

  • A magnetic field is created around the wire
  • the field is made up of concentric circles perpendicular to the wire, with the wire in the centre
• How can the magnetic fields in a wire be shown?

  • place a compass near a wire that is carrying a current
  • as you move the compass, it will trace the direction of the magnetic field
• How does changing the direction of the current affect the magnetic field?

  The direction of the magnetic field changes, use the right hand thumb rule to test it out:

  
• How does the strength of the magnetic field change with the current and distance from the wire?

  The larger the current through the wire, of the closer to the wire you are, the stronger the field is
• What is a solenoid?

  A coil of wire
• How can you increase the strength of the magnetic field that a wire produces?

  By wrapping the wire into a coil called a solenoid:

  
• What does a solenoid wrapping around a wire result in?

  Lots of field lines pointing in the same direction that are very close to each other. The closer together they are, the stronger the field is
• What is the magnetic field like in a solenoid?

  Strong and uniform (it has the same strength and direction at every point in that region
• What is the magnetic field like outside the coil?

  Just like a bar magnet
• How can you increase the field strength of the solenoid even more?

  • By putting a block of iron in the centre of the coil
  • this iron core becomes an induced magnetic whenever current is flowing
• What happens if you stop the current in a solenoid?

  • the magnetic field disappears
  • a solenoid with an iron core is called an electromagnet ( a magnet whose magnetic field can be turned on and off with an electric current)
• What are some of the uses of electromagnets?

  1. in cranes to attract and pick up things made from magnetic materials like iron. They can be turned on to pick up and turned off to be dropped
  2. can be used within other circuits to act as switches:
  3. when the switch in circuit one is closed, it turns on the electromagnet, which attracts the iron contact on the rocker
  4. the rocker pivots and closes the contacts, completing circuit two, and turning on the motor