Lecture 53 - Speed and Back EMF

[@biplabghosh_official]

Sir Thank you so much for this great explanation

[@sridharchitta7321]

What is a dc motor? What is back emf? Isn't it wonderful that when we flip a switch which is wired to a ceiling fan, the fan rotates! Take a moment to visualize the force which acts on the blades to keep them rotating while we are standing on the floor far below the fan. As if it is rotating by an unseen hand! It operates based on the principle that a current-carrying conductor placed in a magnetic field experiences a force and this is what was encapsulated in the Lorentz force law. A description of load torque always accompanies a discussion on motors. The effect of its imposition on motor torque, and how this causes the motor to draw power from the power supply then follows. The phenomenon of how it is the ‘back emf’ in motors, which regulates the motor torque to match load torque completes the discussion. To understand these ideas, it would be instructive to understand Current, the conduction process and Voltage at the fundamental level. Electrostatics and circuits belong to one science not two as in the following two videos: i. kzbin.info/www/bejne/ioXXpWVul5aXj9E and ii. kzbin.info/www/bejne/bnO0fpKurJeFnNE The "back emf" or "motional emf" is a trick nature uses which has a regulating effect in determining the amount of current the motor draws and is a natural consequence of the induced emf process when a conductor moves in a magnetic field. The fan pushes air and the molecules of air when they leave the blades produce a reaction force, a torque as the blades spin. The fan motor should generate sufficient torque to overcome this opposing “load” torque and keep the blades spinning. The "back emf" regulates the current to generate this required torque automatically! The governing relation for current in conductors is J = σE_net where σ is the conductivity of the conductors and E_net is the resultant of the applied and induced electric field components in the conductor. It is not possible in this post to discuss in more detail the process of production of the back emf and its regulating effect on motor torque. The last frame References in video #1 lists textbooks 3 and 4 which discuss these topics in more detail using a unified approach and provide an intuitive understanding of the generation of an emf in generators and motors.

[@muhammedabdullah4110]

thank you so much for your lectures .. god bless u

[@vikasgoswami7613]

very well explained sir... thank you

[@premkumarguntagani8811]

Here we can take peak voltage or rms voltage of back emf

[@uceee1]

do you have any lecture about MTPV?

[@vijayanandganesan4666]

Do we have answers for the assignments given ? Just to verify

[@bibekgautam7644]

thank you