Dynamos & Generators
Spin generator, see AC output. Builds on Faraday's Law.
You look at an electric motor that spins when you connect it to a battery, and an electric generator that produces voltage when you spin its shaft by hand. They look almost identical inside — both have coils of wire and permanent magnets.
Are a motor and a generator fundamentally the same device?
They’re the same device! A coil spinning in a magnetic field generates an EMF (generator mode). Current flowing through a coil in a magnetic field makes it spin (motor mode). The same machine does both. In fact, every running motor is simultaneously acting as a generator — the “back-EMF” it produces opposes the driving voltage.
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Watch the coil rotate in the magnetic field. As it spins, the changing flux creates an AC voltage output. Notice how the EMF depends on the coil’s angle — maximum when the coil is parallel to the field, zero when perpendicular.
ε = NBAω sin(ωt)
The EMF is a sine wave. Spin faster and you get both higher voltage AND higher frequency. That’s why generators at power plants spin at precisely 50 or 60 Hz.
Wind spins the blades, which spin a generator coil inside magnets. The faster the wind, the higher the frequency and voltage — power electronics then convert it to a steady 50/60 Hz for the grid.
A small generator pressed against your tire spins with the wheel. At low speeds the light is dim (low EMF); at high speeds it’s bright. The flicker at low speeds shows the AC nature of the output.
Electric and hybrid cars use their drive motor as a generator when slowing down. The kinetic energy is converted back to electrical energy and stored in the battery. The motor IS the generator.
Whether coal, nuclear, or hydro, the core is the same: heat or falling water spins a turbine, which spins a generator coil. Faraday’s law converts mechanical energy to electrical energy at massive scale.
“A spinning coil in a magnetic field — that’s a generator. Current through a coil in a magnetic field — that’s a motor. Same device, same law, two directions.”
Generator Lab
Build and tune your own generator. Adjust rotation speed, coil area, magnetic field strength, and number of turns. Watch the AC output waveform in real time. Toggle a commutator to see DC output. Power a virtual load and watch brightness respond to your settings.
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Start at low RPM and watch the slow sine wave. Increase RPM — the frequency and amplitude both rise. Now double the turns: the peak voltage doubles. Toggle the commutator to see how AC becomes bumpy DC. Try powering the light bulb — at what RPM does it reach full brightness?
A generator converts mechanical rotation into AC electricity via Faraday’s law. The peak EMF is NBAω, and the frequency matches the rotation rate. Motors and generators are the same device run in opposite directions.