116k views
1 vote
A dc motor with its rotor and field coils connected in series has an internal resistance of 3.2 ω. when running at full load on a 120-v line, the emf in the rotor is 105 v.

User Paritosh
by
8.4k points

1 Answer

3 votes
Missing question: what is the current drawn by the motor from the line?

Solution:
The potential difference between the two ends of the motor is

\Delta V= \epsilon + Ir
where
\epsilon is the emf, I the current and r the internal resistance of the motor.

By re-arranging the equation and using the data of the problem, we can solve to find the current I:

I= (\Delta V-\epsilon)/(r)= (120 V-105 V)/(3.2 \Omega)=4.7 A
User NeilD
by
8.3k points