Charge Velocity and Velocity of Field Propagation
Question : Find the velocity of charge leading to 1 A current which flows in a copper conductor of cross-section 1 cm2 and length 10 km. Free electron density of copper = 8.5 × 1028 per m3. How long will it take the electric charge to travel from one end of the conductor to the other?
Solution.
i = neAν or ν = i/neA
∴ ν= 1/(8.5 × 1028 × 1.6 × 10−19 × 1 × 10−4)
= 7.35 × 10−7 m/s
= 0.735 μm/s
Time taken by the charge to travel conductor length of 10 km is
Now, 1 year = 365 × 24 × 3600 = 31,536,000 s
t = 1.36 × 1010/31,536,000 = 431 years
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