The resistance of the armature windings of DC motor is 5 $\Omega$.The motor is connected to a 120 V line.When the motor is spinning at full speed,it draws a current of 4 A.The bACk EMF at full speed is
A)20 V
B)100 V
C)120 V
D)40 V
E)80 V

Question

Quizplus · Accepted Answer

At full speed, the voltage across the armature windings can be calculated using Ohm's law:

V = IR + E

where V is the applied voltage (120V), I is the current through the windings (4A), R is the resistance of the windings (5Ω), and E is the back EMF.

Solving for E, we get:

E = V - IR
E = 120V - (4A * 5Ω)
E = 100V

Therefore, the back EMF at full speed is 100V, which is choice (B).

The Resistance of the Armature Windings of DC Motor Is Ω\OmegaΩ

The Resistance of the Armature Windings of DC Motor Is $\Omega$