Current Electricity 1 Question 5

5. In a conductor, if the number of conduction electrons per unit volume is 8.5×1028m3 and mean free time is 25fs (femto second), it’s approximate resistivity is (Take, me=9.1×1031kg )

(a) 107Ωm

(b) 105Ωm

(c) 106Ωm

(d) 108Ωm

(2019 Main, 9 April II)

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Solution:

  1. Resistivity of a conductor is

ρ=mene2τ

where, me= mass of electron =9.1×1031kg,

n= free charge density =8.5×1028m3,

τ= mean free time =25fs=25×1015s

and

e= charge of electron =1.6×1019C

Substituting values in Eq. (i), we get

ρ=9.1×10318.5×1028×(1.6×1019)2×25×1015=9.1×1068.5×2.56×25=0.016×106=1.6×108Ωm108Ωm



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