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A battery of emf E drives current through a conductor PQ of length l whose cross-section tapers, the radius shrinking from r1 at P to r2 at Q (r2 < r1). As one travels from the wider end P to the narrower end Q, which statement(s) hold?

1. The drift speed of the electrons increases.
2. The electric field magnitude decreases.
3. The electron current decreases.
4. All of these

Correct answer: The drift speed of the electrons increases.

Solution

Steady-state current is constant along the wire; as the area decreases toward Q, both drift speed and field increase, so only the drift-speed statement is correct.

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