in this module you will learn about an AC generator an AC generator is an electric generator that converts mechanical energy to electrical energy in the form of an alternating EMF or alternating current working principle of an AC generator an AC generator works on the principle of electromagnetic induction in electromagnetic induction when there is a relative motion between a coil and a magnetic field an electric current or EMF is induced in the coil bounce of an AC generator an AC generator has an armature ABCD it is a rectangular coil with many turns wound around a soft iron core a shaft it can be rotated rapidly a fiend magnet it may be a strong permanent magnet with concave poles to slip rings s1 and s2 these are connected to the armature and thus rotate with it two flashes v1 and v2 they provide electrical contact with the slip rings and a load which may be a galvanometer and Shore working of an AC generator when the armature rotates between the poles of the field magnet the magnetic flux linked with the armature changes continuously as a result an EMF is induced in the armature this in turn produces an electric current through the armature and the galvanometer and through the slip rings and the brushes note that the galvanometer needle swings between the negative and positive values this means that an alternating current is flowing through the galvanometer direction of induced current initially the armature ABCD is vertical with its arm a B up + C D down the direction of magnetic field is from left to right as the armature undergoes 1/2 rotation clockwise arm a B moves down while arm C D moves up according to Plumbing's right-hand rule the current will flow in the direction DC B a so the current will flow from b1 to b2 through the galvanometer now during the next half rotation arm a B moves up while arm C D moves down again by Fleming's right-hand rule current will flow in the direction ABCD that is from b2 to be bond through the galvanometer thus the induced current changes its direction every half rotation graphical representation of induced EMF suppose the armature takes T seconds to complete one rotation clockwise at time T is equal to 0 second the armature ABCD is vertical with arm ad R and arm C D down at this position when the armature rotates the rate of change of magnetic flux is momentarily zero hence the induced EMF at this position is zero during the first quarter rotation the induced EMF increases then at time T upon 4 seconds the armature becomes horizontal at this position the rate of change of magnetic flux momentarily attains the maximum value therefore the induced EMF at this position is maximum during the second quarter rotation the induced EMF decreases then at time T upon two the armature again becomes vertical and therefore the induced EMF is zero during the third quarter rotation the induced EMF increases but has an opposite polarity as compared to that of the first half rotation at time 3 T formed four seconds the induced EMF attains its maximum negative value during the fourth quarter rotation the induced EMF decreases and becomes zero momentarily at time T seconds as the armature is vertical once again so the magnitude of the induced EMF is sinusoidal in this module you have learnt an AC generator is an electric generator that converts mechanical energy into electrical energy in the form of alternating EMF or alternating current an AC generator is based on the principle of electromagnetic induction an AC generator consists of an armature a shaft a field magnet slip rings and brushes the graph between the time and EMF generated by an AC generator is sinusoidal