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Grade 10 Advanced About 20 min Version 1 Awaiting review Premium

Motors and generators

A wire carrying a current in a magnetic field feels a force. In an electric motor a coil sits between the poles of magnets: the force pushes one side of the coil up and the other side down, so it turns. A split-ring commutator reverses the current every half turn so it keeps turning the same way. More current, a stronger magnet or more turns make it turn faster; reversing the current reverses its direction. A generator is the same machine run backwards: turning the coil in the field induces a voltage (electromagnetic induction). The faster it turns, the bigger the voltage.

What you will learn

  • Explain how a current-carrying coil in a magnetic field turns.
  • Describe how to change a motor's speed and direction.
  • Explain how a generator produces electricity and what affects its output.

Before you start

  • Know that a current makes a magnetic field and that a moving magnet induces a voltage.

Materials

  • Insulated copper wire wound into a coil on an axle
  • Two magnets (weak pair and strong pair)

Equipment

  • Split-ring commutator and brushes, low-voltage supply, small bulb, hand crank

Procedure

  1. As a motor with the weak magnets, set the supply to 3 V and then 6 V, recording the speed.
  2. Reverse the current and record.
  3. Switch to generator. Turn the crank at 60 and then 240 turns per minute, recording the voltage.
  4. Use the strong magnets and turn the crank at 240 turns per minute again.

How this simulation is simplified

  • Motor speed = 20 × magnet strength × supply voltage turns per minute (weak magnets 1, strong 2), with no load.
  • Generator voltage = 0.01 × magnet strength × turns per minute; the bulb is fully bright at 4.8 V.