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Doubt & Answer Explanation

Doubt

 A potential difference V is applied to a copper wire od diameter d and length l. what is the on the electron drift speed of-
i) doubling l
ii) doubling V
iii) doubling d?

Answer Explanation

i = neAvd

Here i = current, n = number of electrons per unit volume, A = area of cross section and vd = drift velocity.

Therefore, V = iR or V = neAvd R = neAvd x resistivity x l/A. 'A' cancels off and we have V = nelvd x resistivity.

Doubling l, halves the drift speed because it is inversely proportional to l.

Doubling V doubles the drift speed as it is proportional to V.

Doubling d does not change the drift speed as the drift speed does not depend on the area of cross section when the voltage is constant.



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