Motors – GCSE Physics A (Combined) OCR Revision

Basic Principles of Motors

Electric motors convert electrical energy into mechanical energy, powering many everyday devices.
They work using the principle of the motor effect where a current-carrying conductor experiences a force if it is placed in a magnetic field.
The direction of this force is given by Fleming’s Left-Hand Rule which states that if the thumb, index finger and middle finger of your left hand are held at right angles, with the thumb representing motion, index finger representing magnetic field and middle finger representing current, each one points in the direction of the corresponding variable.

DC motors are powered by direct current, like from a battery.
AC motors are powered by alternating current, like from mains electricity.
In a simple DC motor, a coil of wire spins in a magnetic field. The direction of current in the coil is reversed every half a turn by a split ring called a commutator to keep the coil spinning in the same direction.

The size of the force on a current-carrying conductor can be increased by: increasing the current, increasing the strength of the magnetic field, or increasing the length of wire in the magnetic field.

Iron-core armatures are used in magnetic fields to increase motor efficiency.
Using more windings or turns in the coil can also increase motor efficiency.
The efficiency of an electric motor can be improved by reducing friction and electrical resistance within the motor.

Electric motors are used in a wide range of devices, from small battery-powered devices like phones and toys, to large industrial machines.
The principles of electrical motors are also used in generators, which convert mechanical energy into electrical energy. The process for this is nearly the opposite of how motors work.

The interaction of magnetic fields and electric currents forms the basis of many technologies, including speakers, solenoids, and data storage on hard disks.
These applications all depend on the motor effect. Understanding this effect is crucial in understanding how electric motors work.

The formula for the force on a conductor in a magnetic field is F = BIL, where F is the force, B is the magnetic field strength, I is the current, and L is the length of conductor in the field.