Question

A 0.40 mm diameter copper wire carries a current of

3μA. Find the current density and he electron drift density in the wire

Answer 1

Now current density

$J=\frac{I}{A}\\J=\frac{I}{\pi r^2}$

$r=\frac{D}{2}=0.2mm$

$$A=\pi r^2=3.14\times(0.2\times10^{-3})^2=3.14\times4\times10^{-8}$$

$J=\frac{3\times10^{-6}}{3.14\times4\times10^{-8}}=23.88A/m^2$

Drift velocity

$V_d=\frac{J}{ne}$

$$V_d=\frac{23.88}{8.49\times10^{28}\times1.6\times10^{-19}}=4.5\times10^{-9}m/sec$$