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Consider the following statements about the drift velocity of conduction electrons in a metallic conductor: A. As the temperature of the conductor rises, the drift velocity of the electrons decreases. B. The drift velocity varies inversely with the cross-sectional area of the conductor. C. The drift velocity is independent of the potential difference applied across the conductor. D. The drift velocity varies inversely with the length of the conductor. E. As the temperature of the conductor rises, the drift velocity of the electrons increases. Select the correct combination of statements.

1. A and B only
2. A and D only
3. B and E only
4. B and C only

Correct answer: A and D only

Solution

With a fixed applied potential difference, drift velocity v_d = eVtau/(mL) decreases with increasing temperature (A correct) and is inversely proportional to length (D correct); it does depend on V, and the A-dependence holds only at fixed current, not fixed voltage.

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