Answer :



Current in the wire, I= 1A

Cross section of the wire, A= 1mm2=10-6m2

Density of Copper, d=9000 kg m–3

Formula Used

The current due to ‘n’ freely bounded electrons per unit volume with a drift speed ‘Vd’ can be expressed as,

Where ‘A’ is the cross-sectional area of the material through which electrons are passing; and ‘e’ is the charge of the electron, which is


In the given problem, n is not directly given. But we know that 63.5 grams of Copper have Avogadro number (6.022×1023) of atoms. So ‘m’ Kilograms have,

Also, in terms of density, d, the mass m can be replaced in the above expression as,

And for Unit volume, the number of atoms are,

So, the number of free electrons/ atoms are,

From eqn.1, the expression for Drift Velocity, Vd

Substituting the known values, it becomes,

Hence the drift speed of free electrons is 0.074mm/s

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