electrical engineering

They both spin because of the electro repulsive effect. DC direct current uses coils and permanent magnets. AC alternating current uses a voltage that goes positive and then passes through a zero voltage to change polarity to a negative voltage (sign wave) you can also get a square wave where the wave shape is like that of a squared off shape vertical to Begin flat across the top and back down to cross over and go horizontal before going back up again; this repeats for as long as you like.

AC is used because it can be transformed up or down in voltage you can only convert down with DC unless you use a chopper supply.

See this thread.

in Dc motors there is an external field(generated by a parmanent magnet in stator) n another field is created by the rotar conducting dc current.bt dc current in a coil cannot generate a pulsating magnetic field.so a commutator is there 2 convert dc current 2 ac n produce the field..then by the interaction of the two fields toque is generated acc 2 Lenz's law..that causes the motor 2 rotate

AC motors r mainly of 2 typs 1.synchronous 2.induction....in syn motor it is 1st run as gen with dc in rotor(field) n 3 pn in stator(arm)..then it pull into synchonism n aftr it reaches syn speed primmover is switchd off.in induction motor roter is shrt cktd n ac is applied in stator..stator produces an pulsating electromagnatic field which induces an emf in short ckted roter due 2 xfmer action..ths emf causes current in sht cktd rotor which again produces elecmag field..by interaction of 2 roter rotates

AC motors are only used in Air Conditioners. DC motors are only used in the capital city of the United States. Air Conditioners in Washington DC must use AC/DC motors, often called "Universal" motors, which are only found at Universal Studios in Los Angeles.