In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
A)remain unchanged
B)reduce to one-fourth value
C)increase four folds
D)be doubled

Question

Quizplus · Accepted Answer

The torque developed by a DC motor is proportional to the product of the armature current and the magnetic field. When the back EMF is doubled, for a given supply voltage, the armature current reduces to half (since back EMF opposes the supply voltage and reduces the effective voltage across the armature). However, if the speed is also doubled, the back EMF increases proportionally, indicating that the motor is operating more efficiently but does not directly affect the torque produced. The torque remains unchanged because the effect of doubling the speed (which could imply a potential increase in torque due to more energy conversion) is counteracted by the reduction in armature current due to the increased back EMF.

In Case the Back E