With reference to the electron drift speed in a current-carrying conductor, which one of the following statements is correct?
[amp_mcq option1=”It is much more than the average electron speed.” option2=”It is much lesser than the average electron speed.” option3=”It is very close to the average electron speed.” option4=”It is close to the speed of light.” correct=”option2″]
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UPSC Geoscientist – 2022
The average speed of electrons due to their random thermal motion in a conductor at room temperature is very high (on the order of 10⁵ to 10⁶ m/s). When a voltage is applied, the electrons acquire a net drift velocity in the direction opposite to the electric field. This drift speed is typically very low, on the order of millimeters per second (10⁻⁴ to 10⁻³ m/s), much less than their random thermal speed.
In the absence of an electric field, free electrons in a conductor move randomly due to thermal energy, colliding with lattice ions. Their average velocity is zero, but their average speed is high. When an electric field is applied, the electrons experience a force that causes them to accelerate between collisions. Although collisions are frequent, resulting in a zig-zag path, there is a net average velocity in the direction of the force, which is the drift velocity. This drift velocity is responsible for the electric current.