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Difficulty: HardElectrical Current and Electron Flow

In a direct-current (DC) circuit powered by a battery, the physical drift velocity of individual free electrons through a solid copper conductor approaches the speed of light, which directly accounts for the nearly instantaneous delivery of electrical energy to a connected load.

Answer: Answer

Answer

False
The statement is false. Individual free electrons in a copper wire drift at an extremely slow pace—typically less than 1 mm/s1\text{ mm/s}—because of continuous collisions with lattice ions. The virtually instantaneous illumination of a lamp or activation of a load occurs because the electric field travels through the wire at nearly the speed of light, setting all free electrons throughout the circuit into motion almost simultaneously.

Step-by-Step Solution

1
Differentiate between charge carrier drift velocity and electromagnetic field propagation in a conductor.
Drift velocity describes the slow, net physical displacement of electrons through the lattice, whereas field propagation is the speed at which the electromotive force and electric field establish across the circuit.
Understanding electrical current requires distinguishing the physical transport of matter and charge from the propagation of the energy-carrying electromagnetic wave.
2
Analyze the typical magnitude of electron drift velocity (vdv_d) in metallic conductors.
Due to frequent collisions with vibrating copper atoms in the lattice, the net drift velocity of electrons under direct current is on the order of millimeters per second or less (10−4 m/s10^{-4}\text{ m/s} to 10−3 m/s10^{-3}\text{ m/s}).
Thermal motion is fast and random, but the directional drift caused by the applied electric field is very slow.
3
Identify the mechanism responsible for near-instantaneous energy transfer when closing a circuit switch.
When the circuit closes, an electric field propagates through the conductor at a significant fraction of the speed of light (cc), simultaneously exerting a force on all free electrons already present in the wire.
Energy is transferred through the field rather than by individual electrons racing from the source to the load.
4
Evaluate the truth value of the overall technical statement.
Because physical electron drift velocity is microscopic rather than approaching the speed of light, the assertion is false.
The statement erroneously attributes energy delivery speed to physical carrier velocity instead of field propagation.

Key Concept

Electron drift velocity versus electric field propagation in current flow
Estimated Time:45s
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Topics

Electrical Current and Electron Flow

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