1.) A dc motor has coils with a resistance of 15 ? and is connected to an emf of

Question

1.) A dc motor has coils with a resistance of 15 ? and is connected to an emf of 120.0 V. When the motor operates at full speed, the back emf is 72 V

(a) What is the current in the motor when it first starts up?
A

(b) What is the current when the motor is at full speed?
A

(c) If the current is 6.5 A with the motor operating at less than full speed, what is the back emf at that time?

V

2.) The current in a 0.090 H solenoid increases from 20.0 mA to 170.0 mA in 3.0 s. Find the average emf in the solenoid during that time interval.
mV

Explanation / Answer

(a) current =120/15=8 ampere

(b)current when motor is in full speed=(120-72)/15=3.2 ampere

(c) net voltage=6.5*15=97.5

     hence back voltage=120-97.5=22.5 volt

part 2

emf=L di/dt

      =0.09 *150*10-3/3

     = 4.5*10-3

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