Motors and generators
Pass a current through a coil between two magnets to make a motor, then spin the coil by hand to make a generator that lights a bulb.
Core concept
A motor turns electrical energy into movement; a generator turns movement into electrical energy, using the same coil and magnets
Topic: Magnetism
A wire carrying a current: The flow of electricity through a wire, measured in amperes (A). All key words in a magnet: An object that pulls iron and steel towards it. All key words field feels a force: A push or a pull. Forces can start, stop or turn things. All key words. In an electric motor a coil sits between the pole: One of the two ends of a magnet (north and south), where its pull is strongest. All key words 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: The push that makes electricity flow, measured in volts (V). All key words (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
- As a motor with the weak magnets, set the supply to 3 V and then 6 V, recording the speed.
- Reverse the current and record.
- Switch to generator. Turn the crank at 60 and then 240 turns per minute, recording the voltage.
- 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.