At an instant when the current in an alternating-current (AC) circuit passes through zero
PHYSICS · Single correct · CBSE · Physics · Current Electricity · Current Electricity
Problem
At an instant when the current in an alternating-current (AC) circuit passes through zero, a student claims that no electrons are moving in the circuit at that moment. Which of the following best accounts for why the student’s claim is incorrect?
(a) Equal numbers of electrons are momentarily drifting in opposite directions, so their contributions add to zero net current even though each electron is still in motion.
(b) Because the current rating of an ac source is given as an rms value that never reaches zero, electrons maintain a constant average drift speed at all times.
(c) Thermal agitation keeps every electron in rapid random motion even when the electric field (and thus the drift velocity) passes through zero, so electrons never come to rest.
(d) The inductance of the circuit gives the electrons inertia, allowing them to keep moving right through the zero-current crossing so that the current never actually reaches zero in the wire.