Electromag

• split ring commutator

  1. The split-ring commutator swaps the positive and negative connections every half turn.
  2. Therefore, the direction of the current through the coil reverses every half turn.
  3. This means that the forces acting on the coil will always be acting in the same direction.
  4. This causes the coil to rotate continuously in one direction.
• To increase the speed of an electric motor you can add more turns to the coil, use stronger magnets, or increase the current in the coil. 
• You could increase the current, increase the number of turns of wire while keeping the length of the solenoid the same, reduce the length of the solenoid while keeping the number of turns of wire the same, or add a soft iron core.
• To increase the size of an induced potential difference you could use stronger magnets, move the coil or magnetic field faster, or add more turns to the coil. 
• Due to the split ring commutator, dynamos produce direct current.

  Due to the slip rings and brushes, alternators produce alternating current
• electromagnetic induction (generator effect) is used in dynamos.

  A coil of wire is turned inside a magnetic field, which induces a magnetic field, and hence current, in the coil of wire. The coil is connected to a commutator which switches the connections every half-turn. This causes the induced current in the external circuit to be in one direction (d.c.). 
• How loudspeakers work

  1. Alternating current flows through wire

  2. Creates magnetic field (electromagnetism) in coil

  3. Magnetic field of coil interacts with magnetic field of permanent magnet

  4. Interacting magnetic fields exert force on coil (motor effect), causing it to move back or forth along permanent magnet

  5. Causes cone to change shape

  6. As current is alternating, magnetic field and force also alternate

  7. Coil of wire and cone rapidly move back and forth, meaning they vibrate

  8. Cone vibrations cause pressure variations in the air - which are sound waves
• How transformers work

  1. When supplied with an alternating current, the primary coil will generate an alternating magnetic field.
  2. This then induces an alternating magnetic field in the iron core.
  3. This in turn induces an alternating voltage in the secondary coil, which if the circuit is complete will lead to an alternating current.
• How microphones work

  • sound waves hit the diaphragm
  • this causes the diaphragm and coil of wire to move
  • as wire is moving within the magnetic field of the permanent magnet, it will generate a current (electromagnet induction / generator effect)
  • The frequency and amplitude of the soundwaves will determine how much the diaphragm vibrates, and therefore determine the frequency in the amplitude of the current