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A uniform wire of diameter d carries a current of 100 mA when the mean drift velocity of electrons in the wire is v. For a wire of diameter d/2 of the same material to carry a current of 200 mA, the mean drift velocity of electrons in the wire is

Asked in Re-NEET 2024 · Drift velocity, mobility and current density

• (1) 4v
• (2) 8v
• (3) v
• (4) 2v

Step-by-step solution

Why the other options are wrong

• (1) Accounts for the smaller area but forgets that the current is doubled.
• (3) No single slip gives v; both the smaller area and the larger current raise the drift speed.
• (4) Accounts for the doubled current but not the area, which falls to a quarter.

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