electromagnetic induction

• what is needed for a current to flow?

  potential difference (voltage) and the potential difference drives a current round a circuit.
• what happens if a wire (or any electrical conductor) moves near a magnet?

  it induces a potential difference in the conductor.
• what is a changing magnetic field?

  a magnetic field with changing strength.
• if there is a magnetic field through the middle of a coil of wire, it is "linked" with the coil.
• what induces a potential difference in a solenoid?

  moving a bar magnet in and out of a coil of wire.
• in what 2 ways can you induce a bigger potential difference in an electrical conductor?

  • faster movement: making the magnetic field change more rapidly by moving the wire or the magnet more quickly.
  • more coils: increasing the number of turns of coil in a wire.
• what happens if a wire moves downwards into a horseshoe magnet?

  • a potential difference is induced in the wire and an electric current flows through the wire.
  • a force will push the wire upwards, opposing the downwards movement of the wire that induced the potential difference.
• what happens if a wire moves upwards into a horseshoe magnet?

  if the wire was moving upwards to create the potential difference then the force on the wire due to the induced potential difference would push it downwards.
• when a potential difference is induced in a wire what is created?

  a force acting in the opposite direction to the action that induced the potential difference, this is due to the motor effect.
• what are features of the motor effect?

  • the force created acts in the opposite direction to the action which induced the potential difference.
  • it creates a force when a potential difference is induced.
• In which direction does a force induced by the motor effect run?

  In an opposite direction to the inductive force
• what is alternating current (AC) produced by?

  a rotating-coil generator, where a coil of wire is rotated inside a fixed magnetic field.
• how does a rotating-coil generator induce a potential difference?

  when the coil rotates, it cuts across the magnetic field lines and a potential difference is induced. This causes a current to flow in the coil of wire. The faster the coil cuts across the lines, the greater the magnitude (size) of the induced potential difference.
• when the top and the bottom edge of the coil are moving parallel to the magnetic field lines, what is induced?


  the coil doesn't cut across any magnetic field lines so there is no induced potential difference.
• when the top and bottom edge of the coil are moving perpendicular to the magnetic field lines, what is induced?

  at this point the coil cuts across the most field lines, so the magnitude (size) of the induced potential difference is at its highest.
• what is the magnitude of the induced potential difference affected by?

  • the number of field lines the coil cuts through.
  • the angle between the coil and the magnetic field lines.
• what produces a direct current (DC)?

  a dynamo
• what does a dynamo generate?

  the coil rotates which generates a potential difference in one direction.
• what does the split-ring commutator do in a dynamo?

  it reverses the direction of the current every half-turn of the coil. This makes sure that the current is always moving in the same direction to keep the coil rotating.
• in a dynamo, when is the potential difference highest?

  when the coil and the magnetic field are parallel or when the coil "cuts" across the magnetic field at the fastest rate.
• in a dynamo, when is the potential difference zero?

  when the coil is perpendicular (at right angles) to the magnetic field or when the coil does not "cut" the field lines at all.
• how does a microphone work?

  • the sound waves that hit the microphone make a coil inside a magnet vibrate.
  • the coil vibrates at the same frequency as the sound wave coming in.
  • this induces a potential difference and current in the coil.
• What does a microphone convert into electrical energy?

  sound waves