Magnetic Forces on Currents and Charges; the Electric Motor
A magnetic field does not only surround a current — it can push on it.
Big Idea: In the last topic you saw that an electric current creates a magnetic field (Oersted's experiment). Now we turn it around: when a current-carrying wire, or a single moving charge, sits inside a magnetic field, the field pushes on it with a real, measurable force. Control that force cleverly and you can make a wire spin forever — that is an electric motor.
By the end you will be able to:
- state that a magnetic field exerts a force on a current-carrying conductor and calculate it with F = BIl;
- use the left-hand rule to find the direction of that force;
- explain the force on a single moving charge and use F = qvB;
- describe how a direct-current (DC) electric motor turns electrical energy into rotation;
- explain why every motor needs a commutator to keep spinning the same way.