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A straight conductor of uniform cross- section carried a current I. Let s=specific charge of an electron. The momentum of all the free electrons per unit length of the conductor, due to their drift velocities only, is

1. Is
2. \( 1 / s \)
3. \( \sqrt{I / s} \)
4. \( (I / s)^{2} \)

Correct answer: Is

Solution

For a conductor, the drift current is carried by electrons moving with speed v_d, so the momentum per unit length is (number of electrons per unit length) × m v_d. Using I = n e A v_d and specific charge s = e/m, the mass cancels and the result becomes I s.

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