Question

Is back emf AC or DC?

Answer 1

Back EMF (Electromotive Force) can be either AC (Alternating Current) or DC (Direct Current), depending on the type of motor or system you're dealing with.

1. In DC motors: Back EMF is typically DC. When the motor is running, the back EMF generated opposes the applied DC voltage and limits the current flow. The amount of back EMF is proportional to the speed of the motor, and it behaves like a DC voltage that opposes the DC supply voltage.
   

1. In AC motors: Back EMF is usually AC. For example, in an induction motor, the back EMF is alternating because the motor is driven by an alternating current. The back EMF in this case follows the frequency of the AC supply.
   

So, whether back EMF is AC or DC depends on the motor's type and the nature of the supply current.