A copper wire of radius 0.1mm and resistance `1k(Omega)`is connected across a power supply of 20 V.(a)How many electrons are transferred per second between the supply and the wire at one end?(b) Write down the current density in the wire.

Explanation

`r= 0.1mm = (10^-4), `
` R = 1 kOmega = (10^3)Omega, v=20v`
` (a) No. of electrons transferred `
` i= V/R = 20/(10^3)`
` = 20 xx (10^-3) = 2 xx (10^-2) A `
` q = it = q xx (10^-2) xx 1 `
` = 2 xx (10^-2)C `
No. of electrons transfered
` = (2xx (10^-2)/1.6 xx (10^-19)) = (2 xx (10^17)/1.6) `
` = 1.25 xx (10^17)`
` (b) current density of wire
= i/A = (2 xx (10^-2)/3.14 xx (10^-8))`
` = 0.6369 xx (10^-6)`
` = (6.37 xx (10^5)A/m^2).`