Magnetism model answer

• Explain how a dc motor works (4)

  • Loop of wire carrying current placed in magnetic field
  • Current flows in opposite directions on each side of the loop
  • Force is exerted on two sides of loop in opposite directions (fleming’s left hand rule) so loop rotates
  • A split ring commutator reverses the direction of the current in the wire at every half turn so that the loop continues to rotate in the same direction
• How can you increase the speed of a motor? (3)

  1. Increase current
  2. Increase strength of magnetic field
  3. Increase number of turns on coil
• How can you reverse the direction of the motor?

  Reverse direction of current

  Reverse the magnetic field
• How can we work out the direction of the force/movement? (4)

  • Use Fleming’s left-hand rule
  • First finger is direction of magnetic field N to S
  • Second finger is the direction of the current
  • Direction of thumb indicates direction of force
• How can we work out the direction of the force/movement? (4)

  • Use Fleming’s left-hand rule
  • First finger is direction of magnetic field N to S
  • Second finger is the direction of the current
  • Direction of thumb indicates direction of force
• Increasing the strength of the magnetic field around a wire

  1. Coil wire into a solenoid and/or increase number of turns in coil

  • solenoid acts like a bar magnet

  - has North and South poles

  2) Insert iron core

  • Now called an electromagnet

  3) Increase the current
• Permanent magnet

  produces its own magnetic field which is always there

  both attract AND repel magnetic poles
• Induced magnet


  only becomes magnetic when it is in a magnetic field

  Only attract to magnetic poles