what is the main principle of working of dynamopleaseexplain breifly

According to faradays law of electro magnetic induction,whenever a conductor is placed in a
varying magnetic field,an E.M.F.[Electromotive Force]gets induced in the conductor the 
magnitude of induced E.M.F.can be calculated from DC generator. If conductor is provided
with enclosed path,the included current will circulate within the path.In a DC generator,field
coils produce an electromagnetic field  and armature are rotated into the field.The direction of
induced Flemming's Right Hand Rule.

Lets consider an armature rotating clockwise and a conductor at left is moving upward.When
the armature completes half rotation,the direction of motion of that particular conductor will
be reversed to downwards.Hence direction of currentin every armature conductor will be
alternating.So we get undirectional current at terminals..
                                                                                                                             - H.RAJGOPAL