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Two wires of equal cross-sectional radius r but made of different materials are joined end to end (in series) and carry the same current. If the number densities of charge carriers in the two wires are in the ratio 1: 4, what is the ratio of the drift velocities of electrons in the two wires?

1. 4: 1
2. 1: 4
3. 2: 1
4. 1: 2

Correct answer: 4: 1

Solution

Since I = n*A*e*v_d is the same and A is equal, v_d is inversely proportional to n; with n1:n2 = 1:4, v_d ratio = 4:1.

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