Magnetism

• What are the types of forces magnets experience?

  Attraction and repulsion
• What is a permanent magnet?

  A magnet that produces its own magnetic field
• What is an induced magnet?

  A material that becomes a magnet when it is placed in a magnetic field. They always cause a force of attraction. When taken out of a magnetic field, they lose their magnetism.
• What force do like poles exert on each other?

  Repulsion
• What force do unlike poles exert on each other?

  Attraction
• What are the different types of magnetic material?

  • iron
  • steel
  • cobalt
  • nickel
• What is a magnetic field?

  A region around a magnet where a force acts on another magnet or on a magnetic material
• How do you show the direction of magnet fields?

  1. Place iron fillings around a magnet
  2. Showing the direction using compasses
• Where is the strength of the magnetic field the strongest?

  At the poles?
• Evidence that the core of the Earth must be magnetic?

  If we hold the compass away from a magnet, the needle will always point in the North-South direction
• How are electromagnets produced?

  When a current flows through a conducting wire, a magnetic field is produced around the wire
• How can the strength of an electromagnet be increased?

  • Increase the current
  • Increase the number of turns of the coil
  • Use an iron core
• Why are electromagnets useful?

  The strength can be adjusted, and the magnet can be turned on and off.
• What are some used of electromagnets?

  Doorbell
• How does a doorbell work?

  1. The switch is closed when the buzzer is pressed
  2. A magnetic field is now produced by the electromagnet
  3. The iron contact is now attracted towards the magnetic field
  4. When the contact moves towards the magnetic field, the clapper now hits the bell, breaking the circuit
  5. No current, no magnetic field, spring back to its original position
• What is the motor effect?

  When a conductor such as a wire is carrying a current, it experiences a force in a magnetic field
• What do the brushes do on the split-ring?

  The brushes allow the electric current to pass onto the ring
• What does a split-ring commutator?

  Reverses the direction of the current allowing the motor to do a full 180 spin
• What does the 'Thumb' represent in Flemmings left-hand rule?

  Movement of force
• What does the first finger represent in Flemmings left-hand rule?

  Magnetic field (North - South)
• What does the second finger represent in Flemmings's left-hand rule?

  Current (+ to -)
• How does a loudspeaker work?

  1. Current through a coil in the magnetic field causes a force that moves the paper cone
  2. When the current reverses, the force reverses, the paper cone moves in the opposite direction
  3. AC causes the paper cone to vibrate at the same frequency
  4. This produces sound waves in the air
• What is the equation linking Force, Magnetism, and current?

  Force = Magnetic Flux Density x Current x Length of wire