Compare the drift speed obtained above with (a) thermal speed of electrons carrying the current at room temperature and (b) speed of propagation of electric field along the conductor which causes the drift motion.Avogadro's number=`6.0 times 10^26` per kg atom. Boltzmanm constant , `k=1.38 times 10^-23 J.K^-1` mass of electron `=9.1 times 10^-31 kg`.

Explanation

(a) Thermal kinetic energy of electrons at room temperature T is given by
`1/2mv^2=3/2kT`
`therefore` Thermal speed of electrons,
`v=sqrt((3kT)/m)`
Here, `k=1.38 times 10^-23 J.K^-1 ,T=273+27=300K,`
`m=9.1 times 10^-31 kg`.
`thereforev=sqrt((3times1.38times10^-23times300)/(9.1times10^-31))=1.17times10^5m.s^-1`
`thereforev_d/v=(1.1 times 10^-3)/(1.17 times 10^5)=0.9times10^-8approx10^-8`
(b) Electric field propagates with the speed of electromagnetic were (`c=3 times 10^8 m.s^-1`) through the conductor.
`thereforev_d/c=(1.1times10^-3)/(3times10^8)=3.6times10^-12`