What is it?
• A simple AC generator consist of:
– A rectangular coil.
– A magnetic field.
• The coil spins in the magnetic field.
• When the coil is perpendicular to the B-
field induced EMF is at a maximum.
• When the coil is parallel to B-field induced
EMF is 0
• Because ε=BANωcosωt
Power Station Alternators!
• In a power station 3 sets of
coils are used at 120° from
• Each produce an
alternating emf 120° out of
phase from one another.
• The coils don’t spin the
electromagnet (in the
• An EMF is induced in the spinning coil of an
electric motor because the flux linkage
through the coil changes.
• The induced EMF is referred to as a back
EMF because it’s opposed to the p.d.
• Electric power supplied by the source (IV) =
electrical power transferred to the mechanical
power (Iε) + electrical power wasted due to
circuit resistance (I²R).