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An electric generator consists of a rotating rectangular coil placed btw. 2 poles of a permanent magnet. the 2 ends of this coil r connected to the 2 rings R1 ,R2. the inner side of these rings r insulated. the 2 conducting ststionary brushes B1 n B2 r keptpressed separately on the rings R1,R2 r internally attached to an axle . the outer ends of the 2 brushes r connected to the galvanometer to show the flow of current in the external circuit
 When the axla attached to the rings is rotated such that the arm AB moves up in the magnetic field produced by permanent magnet
 suppose the rectangular coil is rotated clockwise in this rrangement by applying flemings right hand rule the induced currents r set up in the arms along the direction AB n CD
 thus an induced current flows in the clockwise direction the current in the external circuit flows in clockwise direction the current in the external circuit flows from B
 to B
 after 1st quarter rotation the 2nd quarter rotation starts
  as a result the direction of induced currentsin both the arms change giving rise to the net induced current in the anti-clockwise direction.
 the current in the external circuit now flows from B1 to B2. so after every half rotation the polarity of the current now flows in the respective arms changes 
such a current which changes direction after equal intervals of time is called ac current

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Sorry opened the account after a realllllly long time
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