Question

Problem 11

Answer 1

Given information

Given:

the lights may dim briefly when a refrigerator motor starts up;

And when an electric heater is turned on, the lights may stay dimmed as long as the heater is on.

To determine, the reason behind this phenomenon and also the difference between the two cases.

Step-by-step explanation

Step 1.

Counter-emf, also known as back emf, is the electromotive force that opposes the change in current which induced it and is proportional to the rotation speed of the motor. In case of a refrigerator, when the motor starts, there is only a small back emf in the circuit which allows a large current to flow to the refrigerator. This large current overburdens the source and reduces the current to all devices on circuit and causes the lights to dim briefly. As the motor speeds up to its normal speed the back emf also increases and the current flow is back to its usual amount which causes the lights to go back to normal.