Question 3: What factors limit the size of the back emf?

ANSWER

The magnitude of the back emf induced in a coil is directly proportional to the rate of change of flux.

• As the rate of change of flux depend upon the speed of the motor, therefore by increasing the speed of the motor will increase the back emf and decreasing its speed will decrease the back emf.
• When load is connected to the motor, its speed decreases. Consequently, the back emf also decreases.
• Back emf also depends upon the strength of the magnetic field. So by changing the strength of the magnetic field, the back emf can be controlled.
• The speed of coil also depends upon the amount of current flow. So by controlling the current, back emf can be controlled.