With the increase in speed of DC motor
A. Back emf increase but line current falls.
B. Back emf falls and line current increase.
C. Both back emf as well as line current increase.
D. Both back emf as well as line current fall.
Answer: A
Share your understanding of this question with the correct explanation.
With the increase in speed of a DC motor, the back electromotive force (EMF) increases, but the line current falls.
The back EMF in a DC motor is generated due to the rotation of the armature in the magnetic field created by the field windings. It is directly proportional to the speed of the motor. As the motor speed increases, the back EMF also increases. This is because the faster rotation generates a stronger counter EMF that opposes the applied voltage.
The line current refers to the current flowing through the motor from the power supply. As the back EMF increases with the speed, it counteracts the applied voltage, reducing the net voltage across the motor’s armature. This reduction in net voltage results in a decrease in line current.
Therefore, the correct answer is A: Back EMF increases, but line current falls.