Motor Effect Simulator | AQA GCSE Physics

DC Motor Model

No motor effect

Magnetic field Conventional current Force on wire Coil ×Current into page •Current out of page

Controls

Current, I 0.0 A Increasing current increases the force on each side of the coil.

Magnetic field strength, B 0.00 T A stronger magnetic field gives a larger motor effect.

Number of turns 1 More turns means more force pairs, so the turning effect is greater.

Reverse directions

Reverse either the current or the field to reverse the force. Reverse both and the motor spins the original way.

Commutator

With a split-ring commutator, the current reverses every half-turn so the coil keeps rotating in the same direction.

0.00 NRelative force on active sides

Very lowTurning effect

0°Coil angle

No rotationPredicted rotation

What is the motor effect?

When a wire carrying a current is placed in a magnetic field, the wire experiences a force. This is called the motor effect. In a coil, the forces on opposite sides act in opposite directions, creating a turning effect or torque.

F = B I L

For a wire at right angles to the magnetic field, the force is increased by increasing the magnetic field strength B, the current I, or the length of wire in the field L. In this simulator, increasing the number of turns acts like increasing the length of wire in the field.

AQA key idea: The force is greatest when the wire is perpendicular to the magnetic field, and zero when the wire is parallel to the field.

Using Fleming’s left-hand rule

Hold your left hand with thumb, first finger and second finger at right angles to each other. The three directions show force, field and current.

ThumbForce / motion

First fingerMagnetic field
N to S

Second fingerConventional current
+ to −

In the animation, use the purple arrows for field and the blue arrows or ×/• symbols for current. Your thumb gives the red force direction on each side of the coil.

For field left to right: current into the page, ×, gives force down. Current out of the page, •, gives force up.

Things to try

Set the current to zero. Explain why the coil stops accelerating.
Increase only the current. What happens to the force and turning effect?
Reverse the current. What happens to the direction of rotation?
Reverse both the current and the magnetic field. Explain why the rotation direction changes or does not change.
Turn the split-ring commutator off. Why does the coil no longer keep rotating smoothly?
Use Fleming’s left-hand rule to predict the force on the left side of the coil.