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A wire of resistance 12 ohms per metre is bent to form a complete circle of radius 10 cm. The resistance between its two diametrically opposite points, A and B, as shown in the figure, is

Asked in CBSE AIPMT 2009 · Wires bent into shapes

• (1) 3 Ω
• (2) 6π Ω
• (3) 6 Ω
• (4) 0.6π Ω

Step-by-step solution

Why the other options are wrong

• (1) No single slip gives this value; 3 Ω is not a multiple of π, yet every resistance here is proportional to the circumference 2π r.
• (2) Takes the radius as 1 m instead of 0.1 m, which makes the answer ten times too big.
• (3) No single slip gives this value; it is the ten-times-too-big 6π with the π also dropped.

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