Electromagnetic Induction

• What happens when an electrical conductor moves relative to a magnetic field?

  A voltage (potential difference) is induced across the conductor.
• What happens to an electrical conductor when there is a change to the magnetic field that it is placed in?

  The voltage is also changed
• How do you produce an electric current using a magnet and a conductor on a small scale?

  • Moving a coil of wire between magnetic poles
  • Moving a magnet within a coil of wire

  Once a voltage is induced, if there us a complete circuit, a current will also be induced
• How is electrical current produced on a large scale?

  An electromagnet is rotated around a coil.
• What factors affect the size of an induced voltage?

  • The number of turns on the coil of wire
  • How strong the magnetic field is
  • The speed of the movement
• What is the requirement for an induced potential difference to cause a current flow?

  The conductor must form a closed loop or be part of a complete circuit.
• What can be said about the direction of the magnetic field produced by an induced current?

  • The direction is such that it opposes the change that induced the current
  • This change is either the movement of the conductor or a change to the field
• What are two ways that the generator effect is used to generate different types of current?

  • In an alternator to produce alternating-current
  • In a dynamo to produce direct current
• How does a dynamo generate current?

  A coil of wire rotates inside a magnetic field. A commutator is used to ensure it continues rotating in the same direction, therefore keeping the current flowing in the same direction (D.C. current)
• How is electromagnetic induction used in alternators to generate alternating current?

  A coil of wire rotates in a magnetic field. The end of this coil is connected to slip rings which will cause the current to change direction while rotating. This means A.C. current is produced.
• What electromagnetic effect does a microphone take advantage of and how?

  • The generator effect
  • It converts the pressure variations in sound waves into alternating current
• How do loudspeakers make use of the motor effect?

  The motor effect is used to convert variations in the current of an electrical circuit into the pressure variation which produces audible sound.
• Explain how a loudspeaker works.

  • A cone wrapped in wire is connected to an A.C. power supply and is placed in a permanent magnetic field
  • When current flows through the wire, it creates a magnetic field which interacts with the permanent field
  • This produces a force which causes the cone to vibrate, producing sound
• How is the pitch of the sound from a loudspeaker changed?

  • The frequency of the A.C current is altered
  • This creates a different frequency of vibration in the cone
• How do microwaves convert sound into electrical signals?

  • Sound produces pressure variation which causes the diaphragm to vibrate
  • A coil of wire is connected to the diaphragm, so as the diaphragm moves, the coil also moves
  • Movement in a magnetic field means a potential difference in induced
  • As there is a complete circuit, a current is also created