In a wire of circular cross-section with radius $r$, free electrons travel with a drift velocity $V$ when a current $I$ flows through the wire. What is the current in another wire of half the radius and of the same material when the drift velocity is $2V$
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(c) From ${v_d} = \frac{i}{{neA}} \Rightarrow i \propto {v_d}A \Rightarrow i \propto {v_d}{r^2}$
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