Why a spinning coil makes AC

A straight wire is swept between the poles of a magnet. Is an EMF induced across the wire?

A generator spins a coil in a magnetic field, and its EMF alternates: the current it drives keeps reversing. The coil spins steadily, one way, and still the current keeps reversing. Why?

Here is one side of the coil, followed through one full turn.

Side X is one of the coil's two long sides.

During the first half-turn, side X sweeps up past the north pole.

A wire sweeping through a field has an EMF induced, and the direction of the motion sets the direction of the induced current.

So during the first half-turn, the current flows one way.

During the second half-turn, side X sweeps down past the south pole. Side X now moves the opposite way through the field, so the induced current flows the opposite way.

Opposite sweeps, opposite current directions: a reversal every half-turn.

In one line: each side of the coil sweeps up past one pole and then down past the other, so the induced direction reverses every half-turn.

That is why a hand-turned generator's lamp brightens and dims as the current alternates.

A demo generator's coil turns steadily. During one half-turn, the current flows clockwise around the circuit. What does the current do during the next half-turn?

Each coil side now sweeps past the other pole, moving the opposite way through the field.

The direction of the motion sets the direction of the induced current.

So the induced direction reverses.

During the next half-turn, the current flows counterclockwise.

Why does the current reverse even though the coil keeps spinning the same way?

Each side of the coil sweeps up past one pole and then down past the other.

Up past one pole and down past the other are opposite motions through the field.

Opposite motions induce opposite current directions.

So the induced direction reverses every half-turn, even at a steady spin.

A coil spins steadily between two poles. What does the induced current's direction do?

A water wheel spins a mill generator's coil. The current reverses every half-turn. Why?

Asha says that even when the coil spins steadily one way, the induced current keeps reversing. Is Asha correct?

Your turn

Mateo watches one side of a generator coil for exactly one full turn. The induced current reverses direction every half-turn. Enter the number of reversals during that one full turn.

Zara spins a coil between two poles, then holds it still, halfway through a turn. What does the induced EMF do while the coil is held still?

In a wind turbine's generator, the current reverses again and again. Which happening causes each reversal?