Electric Generators

• A loop of wire is rotated in a magnetic field.

• Since the angle between the loop and the B-field is changing, the flux is changing.

• Since the magnetic flux is changing an emf is induced.​

Electric Generators

Electric Generators

Where:

N = number of loops

B = magnetic field

A = area of each loop

​ω = angular velocity = 2πf (f = frequency)

t = time in seconds​

emf Produced in a Rotating Planar Coil

AC Generators

• According to Lenz's Law, the current will flow the one direction when the angle is increasing and it will flow the opposite direction when the angle is decreasing.

• These generators are often called alternating current generators.

Back emf

• When a coils is turned in a B-field an emf is produced

• If an electric motor is running, its coil is turning in a B-field

• By Lenz's Law, this emf will oppose the emf used to turn the motor, called back emf.

• It will reduce the voltage across the motor and cause it to draw less current (Remember, V=IR)

• The back emf is proportional to the speed, so when the motor starts it draws max I, but as it speeds up the I decreases.​