Understanding Back EMF: Effects on Parallel and Series Electrical Circuits

[moon2]

Ex:At home, you plug an electric drill into an electrical outlet and turn it on. At the moment you turn on the drill, the lights in the room(wired in parallel to the drill) flicker and dim briefly, but then return to normal after a moment.

notice that the example is wired in parallel, but in series lights will just get dim and stay the same.

what had happened in both of the case and how can i relate this to back emf?

 

[Meir Achuz]

When you turn the electric motor on, there is a surge of current, dimming other lights.
When the motor gets up to speed, there is a back EMF in the circuit which reduces the current through the motor.