What a learner can do afterwards
- Describes how a change in the magnetic field passing through a coil induces voltage, with current flowing if the circuit is closed
- Predicts how faster motion, more coil turns or a stronger magnet can increase induced voltage under matching conditions, and explains when generation stops
- Explains current reversal in a simple AC generator and identifies the mechanical input in a bike generator or power-station generator
1 · Read
Current is flowing charge. A change in the magnetic field passing through a coil induces voltage. A closed circuit allows current. Moving a magnet into or out of a coil can cause this change. A changing nearby electromagnet can do so while the coil stays still. Motion alone is not enough: moving a coil within a uniform field without changing how the field passes through it need not induce voltage. Faraday investigated induction in the 1830s.
Keep the coil, magnet and path the same: faster movement gives a larger induced voltage. A stronger magnet or more turns can also raise voltage when other conditions match. At fixed total resistance, larger voltage gives larger current. Extra turns can also add resistance, so they do not guarantee more current. For a supplied chart, compare its recorded values; do not assume an exact ratio.
A bottle dynamo touches a bike tyre. Wheel rotation turns a magnet near a coil. In a basic lamp circuit without regulation or stored energy, faster rotation can brighten the lamp. A coasting wheel still drives the dynamo after pedaling stops. When rotation stops and the field through the coil becomes steady, generation stops. A lamp with stored energy may stay lit.
In a simple AC generator, a coil rotates between magnet poles. After each half turn, its sides move through the field in opposite directions, reversing voltage and current in a closed lamp circuit. AC means alternating current: its direction repeatedly reverses. Slip rings keep each coil end connected to the same output wire. A battery supplies one-way DC. A commutator or electronics can give a generator a DC output.
Wind, steam or falling water can turn a turbine connected to a generator. Many large generators rotate magnets inside stationary coils. Rotation changes the field passing through the coils. The turbine and bike wheel both supply mechanical input; their generators transfer energy electrically to circuits. Generators do not create energy. A motor has the reverse energy-transfer role: electrical input produces motion through magnetic forces.
A changing field through a coil induces voltage. A closed circuit allows current. Generators need mechanical input. A simple AC generator repeatedly reverses current direction.
Readings and flashcards written for this dataset. The linked video, AC and DC generators, remains the work of its creator.
More to read
What a coil and meter can show
A sensitive current meter can be connected to a coil in a closed loop. When a magnet enters the coil, the meter responds. Hold the magnet still and there is no continuing induced current. Pull the same pole back out and the response reverses.
The important condition is a change in the field passing through the coil. A stationary coil can respond when a nearby electromagnet changes its field. Movement is one way to produce the change, not a requirement in every experiment.
Voltage can be induced even if the coil circuit has a gap. Current around the whole loop needs a closed path. Faraday's experiments in the 1830s helped establish the connection between changing magnetic fields and electrical effects.
Size and direction are different questions
For the same magnet, coil and path, faster movement gives a larger induced voltage. More turns can add voltage when each turn experiences the same field change. A stronger magnet can also increase voltage for matching motion.
Current also depends on the circuit. Adding turns adds wire and may increase resistance. A larger voltage therefore does not always mean a larger current when resistance also changes.
An induced current produces its own magnetic field. Lenz's law describes its direction: this field opposes the change that caused induction. As a north pole approaches a coil, the near face can act as a north pole and repel it. When that pole moves away, the near face can act as a south pole and attract it. Both responses resist the change in the field through the coil.
What turns a generator?
A turbine can receive energy from moving water, wind or steam. Its shaft turns part of a generator. That rotation changes how the magnetic field passes through coils and induces voltage. Many large generators turn magnets while the coils remain fixed.
The electrical output comes from mechanical input. A generator does not create energy. Some input also warms the machine and surroundings. A motor uses electrical input to produce motion, reversing the main energy-transfer role.
A simple rotating-coil AC generator uses slip rings. Each coil end stays connected to the same output wire while the induced voltage reverses each half turn. A connected lamp circuit therefore carries alternating current. Other arrangements use commutators or electronics to provide DC. Solar panels supply electricity without a rotating generator.
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2 · Watch
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Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.