A motor is connected to a 12 V dc supply and draws 5.0 A when it first starts up. What will be the back emf wh

Question

65.) A motor is connected to a 12 V dc supply and draws 5.0 A when it first starts up. What will be the back emf when the motor is operating at full speed and drawing 1.2 A.

A.) 7.8 V

B.) 9.1 V

C.) 10.8 V

D.) 7.0 V

Answer: B please show all steps thanks

Answer 1

5.0A at start up implies a DC resistance of 12V / 5A = 2.4Ω

2.4Ω x 1.2A = an IR loss of 2.9V

12V - 2.9V = 9.1V