Electric Motor & Generator

About this simulation

Electric Motor & Generator is an interactive 3D electromagnetism lab that demonstrates how the same physical machine acts as a DC motor or an AC generator. A rectangular copper coil rotates between permanent North and South magnet poles while green 3D vector arrows display the Lorentz force F = I L x B on each active wire segment. In DC Motor mode, a split-ring commutator reverses the coil current every half-turn so torque tau = N I A B |cos theta| always drives the rotor in the same direction. Clicking a magnet pole switches to AC Generator mode with continuous slip rings, producing a sinusoidal alternating EMF trace on the 3D waveform board.

What students can explore

Watch the green Lorentz force arrows on the two sides of the spinning coil in DC Motor mode and notice how the split-ring commutator flips current every 180 degrees so the left wire is always pushed upward.
Drag the rotor hub by hand through the vertical dead-center position (theta = 90 degrees) to see where torque momentarily drops to zero.
Switch Machine mode to AC Generator (Slip Rings) or click a magnet pole, and compare the full sine wave on the scope board against the rectified DC pulses.
Increase Magnetic field B and Coil turns N with the sliders and verify that both peak torque and induced EMF scale linearly with N and B.
Toggle Magnetic B-field lines on and off to inspect the geometry of I L x B across the air gap.

Learning objectives

1Use the right-hand rule for the Lorentz force F = I L x B to determine the direction of force on each side of a current loop.
2Explain why a DC motor requires a split-ring commutator and brushes to maintain unidirectional torque.
3Contrast the output of a split-ring commutator (rectified pulsed DC) with continuous slip rings (sinusoidal AC).
4Calculate magnetic torque tau = N I A B cos theta and peak generator EMF epsilon_0 = N B A omega.

Questions teachers ask

What is the role of the split-ring commutator in a DC motor?

Without a commutator, the magnetic torque on a current loop would reverse direction every half turn as the wires swap sides between the North and South poles. The split-ring commutator reverses the current direction in the coil every 180 degrees so the torque always pushes in the same rotational direction.

How does an AC generator differ structurally from a DC motor?

An AC generator replaces the split-ring commutator with two continuous slip rings—one connected permanently to each end of the rotating coil—so the induced alternating voltage is delivered directly to the brushes as a smooth sine wave.

At what coil orientation is the magnetic torque maximum and minimum?

Torque is maximum when the plane of the coil is parallel to the magnetic field lines (theta = 0 degrees, cos theta = 1) because the two forces have the largest lever arm. Torque drops to zero when the coil plane is perpendicular to the magnetic field (theta = 90 degrees).

How can you increase the voltage produced by an AC generator?

By Faraday's law (epsilon_peak = N B A omega), you can increase peak voltage by winding more turns N on the coil, using stronger magnets (larger B), increasing the coil area A, or spinning the rotor faster (higher angular velocity omega).

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