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A metallic conductor has a free electron density of 8.5 x 10²⁸ per cubic metre and a mean free time (relaxation time) of 25 fs. Taking the electron mass as 9.1 x 10⁻³¹ kg, the approximate resistivity of the conductor is:

1. 10⁻⁵ Ohm m
2. 10⁻⁶ Ohm m
3. 10⁻⁷ Ohm m
4. 10⁻⁸ Ohm m

Correct answer: 10⁻⁸ Ohm m

Solution

Using the free-electron (Drude) formula, the resistivity comes out near 1.7 x 10⁻⁸ Ohm m, of order 10⁻⁸.

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