Question

Dante drew a diagram of an electric generator.

At top left a piece of magnet labeled N and at top right a piece labeled S. Between these a square coil of wire X sits attached to a metal rod, which runs between the 2 pieces of magnet. A circular piece metal labeled slip ring surrounds the rod at its opposite end from the pieces of magnet and attaches to the square coil. The slip ring has 2 brushes attached to it. Wires connect each brush to a terminal of a meter.
Which best describes Dante’s error?

There should be a battery connected to the brushes.
There should be one brush on each slip ring.
The slip rings should be touching each other.
The magnets should be above the armature and axle.

Answer 1

There should be one brush on each slip ring.

In a generator each end of the coil is connected to its own slip ring, and each brush contacts a different ring so the rotating coil's emf is transferred to the external circuit. Dante shows a single slip ring with two brushes, which would not pick up a potential difference.