A motor has coils with a resistance of 27 and operates from a voltage of242 V. W

Question

A motor has coils with a resistance of 27 and operates from a voltage of242 V. When the motor is operating atits maximum speed, the back emf is 148V. (a) Find the current in the coils when themotor is first turned on.
1 A
(b) Find the current in the coils when the motor has reachedmaximum speed.
2 A
(c) If the current in the motor were 4.0 A at some instant, what is the back emf atthat time?
3 V
(a) Find the current in the coils when themotor is first turned on.
1 A
(b) Find the current in the coils when the motor has reachedmaximum speed.
2 A
(c) If the current in the motor were 4.0 A at some instant, what is the back emf atthat time?
3 V

Explanation / Answer

   E   =   Eback  +   I* R    E   =   AppliedEMF,   Eback   =   BackEMF,   I   =   Instantaneouscurrent,   R   =   Coilresistance    a.   At startup,   Eback   =   0    =>   242   =   0   +   I0* 27          I0   =   242/27   =   8.96   A    b.   When opertaing atmaximumspeed   Eback   =   148   V       =>   242   =   148   +   I* 27       Current   I   =   (242- 148 ) /27   =   3.48   A    c.   When       I   =   4   A          242   =   Eback   +   4* 27          BackEMF   Eback   =   242   -   108   =   134   V

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