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Ankita Katdare
Ankita Katdare • Mar 4, 2007

What is torque and back emf in DC Motors?

Hi all, I want to know what is torque and back emf in DC motors. Please explain in brief.
integratdbrains • Mar 4, 2007
This should clear your understanding 😀

A Torque is generated with combination of forces.In case of a DC motor these forces are generated by the interaction between the fixed field and rotating field.I know you will be clear with what is fixed field and rotating feild.If not feel free to ask.A very wrong notion that exists in every students mind is that, Back EMF is an evil force. It is not so back emf is used to control the speed (typical eg is trains! )
Back EMF is directly related with the EMF.The difference between the applied voltage and the back EMF is known as net voltage. Now with net voltage change the current in the motor changes.. Hence when the motor speed is zero,the back-EMF is zero.
(Had i known which year you are into i would have helped you in a much better way. If you are looking for more clarifications,mail it to me on namrata at
lalit.joshi • Feb 7, 2012
hey, this sounds very interesting. i am very glad, ew are a crazy computer science engineer yet interested in electrical machines. well..... listen, what is torque? when a dc machine is loaded either as a moter or generator, the roter conductors carry current. these conductors lie in the magnetic field of the air gap. due to which each conductor experiences a force and ew can find the direction of force by using feradey's rule. this force is called torque... in rotating electrical machines, torque is of two types....
1. electromagnetic or interaction
2. reluctance or alignment
whereas , when the moter armature rotates, its conductors cut the magnetic flux. hence, the emf of rotation is induced in them. in case of moter this is called back emf or counter emf.
for more info ew can contact me.... at
i have explained shortly. if i committed any mistake, please parden me[​IMG]

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