Electromagnetism and Electric Motors

Study Notes

Current-carrying conductors create a magnetic field, known as electromagnetism.
Magnetic field strength can be controlled by changing the current and is measured in flux lines.
Conductors with opposing currents move away from each other, while those with the same current move towards each other.
Coils of wire can create a stronger magnetic field, and if combined with a soft iron core, become electromagnets.
Induced voltage is created by relative motion between a conductor and magnetic flux lines, known as electromagnetic induction.
Induced voltage depends on the rate at which flux lines are broken by the conductor.
The direction of induced current is determined by Lenz's law and opposes the motion that induced the current.
Electric motor power is measured in kilowatts (kW) and horsepower (hp).
Electric motors work on the principle of electromagnetism, with the rotor and stator containing electromagnets.
The strength of the magnetic field in an electric motor is increased with the current flow.
A DC motor uses a rotating armature in the form of an electromagnet with two poles.
The commutator reverses the direction of the electric current twice every cycle to push and pull against the permanent magnets on the outside of the motor.
DC motor speed depends on the voltage and current flowing in the motor coils and the motor load or braking torque.
The speed of the motor is proportional to the applied voltage, and the torque is proportional to the applied current.
The speed is typically controlled by altering the voltage or current flow by using taps in the motor windings or by using a variable voltage supply.
The speed can also be controlled by using an electronic circuit that switches the supply voltage on and off very rapidly.
The use of brushes in an electric motor has many disadvantages, including electrical noise and requiring replacement.
The horsepower of an all-wheel-drive electric vehicle does not add up because of the total energy the high-voltage battery can supply.
The battery management system is only capable of supplying 380 horsepower worth of energy even though the electric motors themselves are capable of producing more power individually.
The torque of a starter is determined by the strength of the magnetic fields, which is measured in ampere-turns.