How does an AC generator work?

How does an AC generator work?

• A. A simple ac generator consists of a coil rotated in a magnetic field. As the coil rotates the magnetic flux through it changes continuously, inducing a voltage that reverses sign every half rotation, producing AC.
• B. A stationary coil with a rotating capacitor causing alternating current.
• C. A coil rotated in a static electric field yields DC.
• D. A magnet moves around a stationary coil producing alternating current via rectification.

Answer: (A)

Electromagnetic induction drives AC generation: a conductor experiences an emf whenever the magnetic flux through it changes with time. When a coil rotates in a fixed magnetic field, the angle between the field and the coil’s area changes continuously, so the magnetic flux through the coil varies sinusoidally. The induced voltage is proportional to the time rate of change of that flux, which makes the voltage swing in polarity each half turn, giving an alternating output. The rotation speed sets the frequency of the output, and the mechanical work turning the rotor supplies the energy. In practice, the coil’s leads use slip rings and brushes to deliver the AC to the external circuit. Other scenarios don’t fit because a stationary capacitor in motion doesn’t create a changing magnetic flux; a coil in a static electric field doesn’t produce a changing magnetic flux either; and saying the magnet’s motion induces AC “via rectification” is misleading, since rectification converts AC to DC rather than generate AC.

Electromagnetic induction drives AC generation: a conductor experiences an emf whenever the magnetic flux through it changes with time. When a coil rotates in a fixed magnetic field, the angle between the field and the coil’s area changes continuously, so the magnetic flux through the coil varies sinusoidally. The induced voltage is proportional to the time rate of change of that flux, which makes the voltage swing in polarity each half turn, giving an alternating output. The rotation speed sets the frequency of the output, and the mechanical work turning the rotor supplies the energy. In practice, the coil’s leads use slip rings and brushes to deliver the AC to the external circuit.

Other scenarios don’t fit because a stationary capacitor in motion doesn’t create a changing magnetic flux; a coil in a static electric field doesn’t produce a changing magnetic flux either; and saying the magnet’s motion induces AC “via rectification” is misleading, since rectification converts AC to DC rather than generate AC.