p7 - magnetism and electromagnetism

• at which part of a magnet are the magnetic forces strongest?

  the poles of the magnet
• what happens when two magnets are brought close to each other?

  they exert a force on each other
• which type of force is exerted if two like poles of a magnet are brought near each other?

  repulsive, non-contact force
• what type of force is exerted if two unlike poles of magnet are brought near each other?

  attractive, non-contact force
• what is the difference between a permanent magnet and an induced magnet?

  • permanent magnet produces its own magnetic field
  • induced magnet becomes magnetic when placed in a magnetic field
• what type of force does induced magnetism always cause?

  a force of attraction
• what happens when an induced magnet is removed from a magnetic field?

  the induced magnet loses most/all of its magnetism
• what is a magnetic field?

  the region surrounding a magnet where another magnet or magnetic material experiences a non-contact force
• four examples of magnetic materials

  1. nickel
  2. cobalt
  3. iron
  4. steel
• what can always be said about the force between a magnet and a magnetic material?

  it is always attractive
• how does the strength of a magnetic field alter as you move further away from the magnet producing it?

  the magnetic field strength decreases the further you move away
• what is electromagnetism?

  when an electrical current flows through a wire, a magnetic field is produced
• what is a solenoid?

  coil of wire with a strong uniform magnetic field inside it
• what is an electromagnet?

  a solenoid with an iron core inside
• give 4 ways to increase the strength of a solenoid

  1. increase the current
  2. increase the number of turns in the solenoid, while keeping the length the same.
  3. reduce the length of the solenoid while keeping the number of turns the same
  4. add a soft iron core
• how could you change the direction of the magnetic field?

  change the direction of the current
• what does an electric motor do?

  use electricity to create rotational motion
• what is the device commonly used in electric motors

  split-ring commutator
• how does a split ring commutator ensure the coil rotates in one direction?

  • the split-ring commutator swaps the positive and negative connections every half turn, meaning the direction of the current through the coil reverses every half turn.
  • this means that the forces acting on the coil will always be acting in the same direction.
  • this causes the coil to rotate continuously in one direction
• give four ways to increase the speed of rotation in a electric motor

  • increase the current
  • add more turns to the coil
  • increase the magnetic flux density by using more stronger magnets
  • add a soft iron core to the coil