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 ?
Solution and Explanation
Although the drift velocity of electrons is very small (only a few mm/s), the electric field produced by the battery is established throughout the conducting wire almost immediately after the circuit is closed.
This electric field propagates through the circuit nearly with the speed of light. As soon as the field reaches the free electrons present everywhere in the conductor, they start drifting simultaneously.
Thus, the current appears almost instantaneously throughout the circuit, even though an individual electron moves very slowly.
Therefore:
- The electrons do not travel from the battery to the bulb instantly.
- The electric field is established almost instantly.
- All free electrons in the conductor begin drifting at the same time, establishing the current immediately.
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Top CBSE CLASS XII Drift of Electrons and the Origin of Resistivity Questions
Consider a cylindrical conductor of length $l$ and area of cross-section $A$. Current $I$ is maintained in the conductor and electrons drift with velocity $\vec{v}_d$ ($|\vec{v}_d| = \frac{e|\vec{E}|}{m}\tau$), (where symbols have their usual meanings). Show that the conductivity $\sigma$ of the material of the conductor is given by
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Consider a cylindrical conductor of length $l$ and area of cross-section $A$. Current $I$ is maintained in the conductor and electrons drift with velocity $\vec{v}_d$ ($|\vec{v}_d| = \frac{e|\vec{E}|}{m}\tau$), (where symbols have their usual meanings). Show that the conductivity $\sigma$ of the material of the conductor is given by
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- 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 ?
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