Motors, Generators, and Induction

Objective: Explain how a current in a field can produce rotational motion.

A current-carrying conductor in a magnetic field can experience a force, with direction dependent on current and field orientation. In a motor, forces on parts of a current-carrying coil can create torque and rotation; commutation or electronic control maintains useful turning over cycles. An electric motor converts electrical input into mechanical output and other energy transfers such as heating and sound. It does not create motion without an energy input. Motor output depends on current, field, geometry, load, and losses. The local magnetic force may be perpendicular to current direction, so simply saying the field pulls the wire “along the current” is inaccurate.

Objective: Relate changing magnetic flux to an induced potential difference.

Faraday’s law states that a changing magnetic flux through a conducting loop induces an electromotive force; in an introductory model, the magnitude increases with faster flux change and more turns. Flux can change by moving a magnet, moving a coil, changing field strength, or changing orientation. A stationary magnet and stationary loop with constant flux produce no sustained induced voltage from this mechanism. Lenz’s law describes induced-current direction as opposing the change that produced it, consistent with energy conservation. Induction does not guarantee current unless a conducting path is closed. An induced emf is a voltage-like energy-per-charge quantity, not energy created from nothing.

Objective: Compare induction devices and distinguish AC voltage conversion.

A generator uses mechanical input to change magnetic flux through conducting coils and produce electrical output. A transformer uses changing magnetic flux between coils to transfer electrical energy and alter alternating voltage; in an ideal transformer V_s/V_p = N_s/N_p, with approximately conserved power, so higher voltage generally corresponds to lower current at a given power. A transformer does not operate in its standard form with constant direct current after transients. A 100-turn primary and 200-turn secondary under ideal AC conditions doubles secondary voltage. Real devices have losses and rated limits. Motors, generators, and transformers share electromagnetic principles but serve different conversion roles.