Question

why do DC motors require a resistance in relation to back emf? i.e. why do some washing machines when turned on dim the lights?

Answer 1

Explain your question first DC motor's requirement of resistance in relationt to back EMF.

Answer 2

and when a motor anyone either DC or AC, at starting there is no Back emf to oppose the main current, so the a huge amount of current depent on resistance is drawn, hence, a great amount of power loss as P=I^2 R, and after the motor is starting, back emf is set up and an opposing current opposes the main current so, hence less power dissipation and drawing, so when starting motor it the lights and fan gets deem