Question

A copper wire of $3 \, mm^{2}$ cross-sectional area carries a current $5A$ . The magnitude of the drift velocity for the electrons in the wire is (Assume each copper atom contributes one free electron and density of copper $=8920 \, kgm^{- 3}$ , $M_{Cu}=63.5kgmol^{- 1}$ )

• A. $0.24ms^{- 1}$
• B. $0.12 \, m \, s^{- 1}$
• C. $2.4ms^{- 1}$
• D. $0.06ms^{- 1}$

Answer 1

Answer: (B)

Given, $A=3\times 10^{- 6}m^{2},I=5A,$
$M_{Cu}=63.5kgmol^{- 1}$
$\rho _{C u}=8920kgm^{- 3}$
Electron density $=\frac{6.023 \times 10^{23} \times 8920}{63.5}$
$=8.46\times 10^{25}m^{- 3}$
$\therefore $ Drift velocity, $v_{d}=\frac{I}{e n A}$
$=\frac{5}{1.6 \times 10^{- 19} \times 8.46 \times 10^{25} \times 3 \times 10^{- 6}}$
$=\frac{5}{40.608}$
$=0.12ms^{- 1}$