I have a h/w question regarding the current in the armature of a motor when it is operating at half it's normal speed. The question is;
A motor is designed to operate at 118V and draws a current of 12A when it first starts up. At it's normal operating speed, the motor draws a current of 2A. Compute:
a) the resistance of the armature of the coil.
b) the back emf developed at normal speed.
c) the current drawn by the motor at half the normal speed.
I have done parts a) and b) but I don't know how to complete c).
My reasoning goes like this;
Voltage is a measure of how 'hard' you push the current around a circuit, so decreasing the voltage will decrease the amount of current in the circuit (since current is coulomb's per second) which will in turn result in a smaller magnetic force on the armature and hence the motor will be running at a lower speed. But I don't know how to quantify this - All I have managed to find online is that angular velocity is directly proportional to voltage...
I would really appreciate a general discussion of the concepts I need to understand to answer this question.