The resistance of a wire is R. It is bent at the middle by 180^∘ and both ends are twisted together to make a short of the new wire. The resistance of the new wire is
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Bending and twisting often create parallel paths for current.
Step 1: Original resistance:
R = ρ (L)/(A)
Step 2: After bending, wire forms two equal halves in parallel, each of length L/2.
Resistance of each half:
R' = (R)/(2)
Step 3: Parallel combination:
1/Rₑq = (1)/(R') + (1)/(R') = (2)/(R')
⟹ Rₑq = (R')/(2) = (R)/(4)