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When a wire of uniform cross-section a, length l and resistance R is bent into a complete circle, the resistance between any two diametrically opposite points will be

Asked in CBSE AIPMT 2005 · Wires bent into shapes

• (1) R/4
• (2) 4R
• (3) R/8
• (4) R/2

Step-by-step solution

Why the other options are wrong

• (2) Inverts the result: multiplies by 4 where the two halves in parallel divide by 4.
• (3) No single slip gives this value; it would need each semicircle to be R/4, but each half of the wire is R/2.
• (4) Takes one semicircle only and forgets the second half in parallel.

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