Question

Answer the following giving reason:

The electron drift speed is estimated to be only a few mm/s for currents in the range of a few amperes. How, then, is the current established almost the instant a circuit is closed?

Answer 1

1. When closing the switch, an electric field is generated throughout the circuit at the velocity of an electromagnetic wave (about 3 × 10⁸ m/s).
2. This field applies a force on the free electrons located at each location in the wire at that specific moment.
3. As a result, electrons throughout the whole loop begin to drift simultaneously, irrespective of their proximity to the power source.
4. Although the slow movement of each electron (drift speed ∼ 10⁻³ m/s), the “impulse” propagates to every segment of the circuit nearly immediately.