Question:

The number of free electrons per 100mm 100 \,mm of ordinary copper wire is 2??1021 2 ??10^{21} . Average drift speed of electrons is 0.25mm/s 0.25\, mm/s . The current flowing is :

Updated On: Jun 20, 2022
  • 5A 5\,A
  • 80A 80\,A
  • 8A 8\,A
  • 0.8A 0.8\,A
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The Correct Option is D

Solution and Explanation

Drift velocity is defined as the average velocity that a particle attains due to an electric field.
vd=ineAv_{d}=\frac{i}{ne \,A}
where ii is current, nn the number of electrons, ee the electron charge and AA the area of crosssection of wire.
Number of electrons per unit volume
n=2×1021A×100n=\frac{2 \times 10^{21}}{A \times 100}
Hence, current in the wire
i=neAvd i=ne \,A v_{d}
i=2×1021A×100×1.6×1019×A×0.25i=\frac{2 \times 10^{21}}{A \times 100} \times 1.6 \times 10^{-19} \times A \times 0.25
i=0.8Ai=0.8\, A
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Concepts Used:

Electric Current

Defining Electric Current

It is the rate of flow of electrons in a conductor. SI Unit - Ampere (A).

Electrons are negatively charged particles hence when they move a number of charges moves.

Note:- The ability of a particular substance to conduct electricity depends on the number of electrons that are able to move . Some of the materials allow current to flow better than others. 

What is an Electromotive Force?

If a force acts on electrons to make them move in a particular direction, then up to some extent random motion of the electrons will be eliminated. An overall movement in one direction. The force which acts on the electrons to move them in a certain direction is known as electromotive force and its quantity is known as voltage and is measured in V.