Question

If the radius of a copper wire carrying a current is doubled, the drift velocity of the electrons will

• A. remain same
• B. increase four times
• C. decrease four times
• D. increase first and then will decrease

Answer 1

Answer: (C)

decrease four times

Using the relation $I=n\times e\times A\times V_d$,
If current is kept constant then we can see that drift velocity is inversely proportional to area of cross-section of wire. Hence inversely proportional to square of radius of wire , which means that doubling the radius of wire will decrease the drift velocity by a factor of four.