Magnetism and electromagnetism

• What are the poles of a magnet?

  Places where magnetic forces are strongest
• What happens when two like poles of magnets are brought together?

  They repel each other
• What occurs when two unlike poles of magnets are brought together?

  They attract each other
• What type of force is attraction and repulsion between magnetic poles?

  Non-contact force
• What does a permanent magnet do?

  Produces its own magnetic field
• What is an induced magnet?

  A material that becomes a magnet in a field
• What happens to an induced magnet when removed from a magnetic field?

  It loses most/all of its magnetism quickly
• What are the key differences between permanent and induced magnets?

  • Permanent magnets produce their own field
  • Induced magnets require an external field
  • Induced magnets lose magnetism when removed from the field
• What is a magnetic field?

  Region where a force acts on magnets
• What is the force between a magnet and a magnetic material?

  Always one of attraction
• How does the strength of a magnetic field change with distance?

  It decreases with distance from the magnet
• Where is the magnetic field strongest?

  At the poles of the magnet
• How is the direction of a magnetic field determined?

  By the force on a north pole placed there
• What does a magnetic compass contain?

  A small bar magnet
• What does the compass needle point to?

  The direction of Earth's magnetic field
• How can you plot the magnetic field pattern of a magnet using a compass?

  1. Place the compass near the magnet
  2. Mark the direction of the needle
  3. Move the compass around the magnet
  4. Connect the points to visualize the field
• What is the magnetic field pattern of a bar magnet?

  • Field lines emerge from the north pole
  • Field lines enter the south pole
  • Strength varies with distance from the magnet
• How does a solenoid increase the strength of a magnetic field?

  By shaping the wire into a coil
• What is the magnetic field like inside a solenoid?

  Strong and uniform
• How does adding an iron core affect a solenoid's magnetic field?

  It increases the strength of the magnetic field
• What is an electromagnet?

  A solenoid with an iron core
• What is the motor effect?

  Force between a conductor and magnetic field
• What does Fleming's left-hand rule represent?

  Orientation of force, current, and magnetic field
• What units are used for force, magnetic flux density, current, and length?

  N, T, A, m respectively
• What happens to a coil of wire carrying current in a magnetic field?

  It tends to rotate
• How do loudspeakers use the motor effect?

  Convert current variations to sound pressure variations
• What induces a potential difference in a conductor?

  Movement relative to a magnetic field
• What is the generator effect?

  Induced current from movement in a magnetic field
• What does an induced current generate?

  A magnetic field opposing the original change
• What are the factors affecting induced potential difference/current?

  • Speed of movement relative to the field
  • Strength of the magnetic field
  • Angle of the conductor to the field
• How is the generator effect used in alternators and dynamos?

  • Alternators generate AC
  • Dynamos generate DC
• How do microphones use the generator effect?

  Convert sound pressure variations to current variations
• What is a basic transformer composed of?

  • Primary coil
  • Secondary coil
  • Iron core
• Why is iron used in transformers?

  It is easily magnetised
• What does the ratio of potential differences in a transformer depend on?

  Ratio of the number of turns on each coil
• What is a step-up transformer?

  Where $V_s > V_p$
• What is a step-down transformer?

  Where $V_s < V_p$
• What happens if transformers are 100% efficient?

  Power output equals power input
• What is the equation for power in transformers?

  $V_s \times I_s =$$V_p \times I_p$
• How does an alternating current induce a current in another coil in transformers?

  • Alternating current creates a changing magnetic field
  • This induces a current in the secondary coil