Final answer:
When a motor starts, it initially draws more current due to zero back emf, which can cause lights in the same circuit to dim. As it speeds up, back emf increases, reducing the current draw, stabilizing the electrical load and restoring light brightness.
Step-by-step explanation:
When a certain motor is started, it is noticed that the frame begins to experience an increase in current draw, which can sometimes lead to a noticeable effect such as lights dimming in the same circuit. This happens because, at the moment the motor is switched on, the back electromotive force (emf) is essentially zero, allowing maximum current to flow through the motor. As the motor starts to turn, the back emf increases and gradually reduces the amount of current drawn, which stabilizes the electrical load and the lights return to their normal brightness.
This initial high current draw is due to the lack of back emf when the motor's coil is not yet moving in the magnetic field. As the motor speeds up, back emf builds up and opposes the driving emf, hence reducing the current until it reaches a stable operating level, sufficient to overcome only the friction in the system. This concept is important when considering the various electrical appliances that we use every day, such as refrigerators, washing machines, and electric vehicles.