AC Generator — Flashcards & Quiz

Q1: How does an AC generator work?

A coil rotates in a magnetic field. As it rotates, the magnetic flux through the coil changes continuously, inducing an alternating EMF (Faraday's law). Slip rings and brushes maintain continuous contact. The EMF varies sinusoidally: ε = NBAω sinωt, maximum when the coil is parallel to B.

Q2: What is the difference between an AC generator and a DC generator?

AC generator uses slip rings — continuous rings that maintain contact, producing alternating current. DC generator uses a split-ring commutator — reverses connections every half turn, converting AC to pulsating DC. Both work by electromagnetic induction (rotating coil in a magnetic field).

Q3: What is the role of slip rings in an AC generator?

Slip rings are continuous metal rings attached to the rotating coil, each connected to one end of the coil. Brushes (carbon or metal) maintain electrical contact as the rings rotate. They transfer the induced AC to the external circuit WITHOUT reversing the current (unlike a split-ring commutator). This preserves the alternating nature of the output.

Q1: In an AC generator, the EMF is maximum when the coil is perpendicular to the magnetic field.

Answer: FALSE

EMF is maximum when the coil is PARALLEL to B (rate of change of flux is greatest). When the coil is perpendicular to B, flux is maximum but its rate of change is zero, so EMF = 0.

Q2: The output of an AC generator is a sinusoidal waveform.

Answer: TRUE

As the coil rotates at constant angular velocity, the flux changes sinusoidally: Φ = BAcosωt. The induced EMF ε = NBAωsinωt is a sine wave with frequency equal to the rotation frequency.