A fan, a washing machine and a toy car all have a motor. In this course we find that a magnetic field pushes on a wire that carries a current, we find the direction of the push with Fleming's left-hand rule, and we see how this push turns the coil of an electric motor.
3 lessons, about 1 h 15 min3 simulations12 problems6 practice questionsPython in every lesson
Created by StemPy LabA conductor that carries a current in a magnetic field feels a force. The force is the largest when the current is at right angles to the field, and its direction is at right angles to both. Fleming's left-hand rule gives the direction: the forefinger for the field, the middle finger for the current, and the thumb for the force. The size of the force is when the wire is at right angles to the field.
An electric motor changes electrical energy into mechanical energy. A coil in a magnetic field has forces of opposite directions on its two long sides, so it turns. The split ring, called the commutator, reverses the current in the coil every half turn, so the coil keeps turning the same way. The motor is stronger with more turns, a stronger field, a larger current and a soft iron core.
The force on a current in a magnetic field has many uses. A moving-coil galvanometer uses it to measure a current, and a loudspeaker uses it to change a varying current into sound. A moving-coil microphone uses the opposite idea: a sound makes a current.
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