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Question
State microscopic form of Ohm’s law.
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Solution
Current density J at a point in a conductor is the amount of current flowing per unit area of the conductor around that point provided the area is held in a direction normal to the current.
J = `I/"A"`
Drift velocity, `"V"_"d" = "eE"/"m" tau`
I = `"neAV"_"d" = "neA" ("eA"/"m") tau ...["J" = "I"/"A"; sigma = ("ne"^2 tau)/"m"]`
`"I"/"A" = (("ne"^2tau)/"m")`E
J = σE
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