Class 12th Physics 2017 Set3 Delhi Board Paper Solution
Derive an expression for drift velocity of electrons in a conductor. Hence, deduce Ohm's law.
Consider an electron of mass m and charge e moving inside a conductor with a drift velocity Vd when an electic field E is applied. (E = V/l)
Force on electron = -Ee
Acceleration of each electron = − Ee / m
Mechanical force on electron = ma
Velocity created due to this acceleration = Ee / m τ
where, τ is the time span between two consecutive collision. This ultimately becomes the drift velocity in steady state.
We know that current in the conductor i = neA Vd (n is no of free electrons in a conductor per unit volume)
This is as per Ohm's Law.
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