Inducing a current using a magnet. Image credit

Inducing a current using a magnet. Image credit

ZIMSEC O Level Combined Science Notes: Introduction:Motors and generators

  • Electromagnetic induction- is the production of a voltage across an wires (electrical conductor )due to its dynamic interaction with a magnetic field.
  • If a magnet is inserted into a coil of wire connected to an electrical meter
  • A current is induced(created) in the coil
  • The electrical meter is known as a galvanometer
  • A galvanometer is an instrument for detecting and measuring small electric currents
  • When the magnet is pulled out of the coil
  • A current is induced again but in the opposite direction
  • This is shown on the galvanometer with the needle moving in the opposite direction
  • When compared to the direction it takes when the magnet is inserted
  • Induction happens because of the lines of force around a magnet
  • These lines “cut” the wires of the coil
  • The greater the rate of cutting the lines of magnetic force by the coil
  • The greater the current that is produced
  • The size of the current induced(produced/created) thus depends on:
  • The rate at which the magnet moves in the coil
  • The faster the coil moves the greater the current and vice versa
  • The current also depends on the strength of the magnet
  • The stronger the magnet the greater the current
  • The number of turns in the coil
  • The more turns there are the greater the current
  • If the magnet remains stationary in the coil no current is created
  • The current is only created when the magnet is inserted and pulled out of the coil
  • For current to be generated there has to be constant movement (flux) between the coil and the magnet(s)
  • In real world generators it is the coil that is moved inside a stationary movement
  • The coil is attached to turbines which are moved by water, wind, steam, fossil fuel motors etc
  • Generators can either produce Alternating current or Direct current
  • Alternating current constantly changes direction as the coil moves
  • Direct current only flows in one direction
  • Cells and batteries produce direct current

To access more topics go to the Combined Science Notes page.

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