Physics
A copper wire of radius r and length l has a resistance of R. A second copper wire with radius 2r and length l is taken and the two wires are joined in a parallel combination. The resultant resistance of the parallel combination of the two wires will be
5 R
5 R/4
4 R/5
R/5
R/5
1st copper wire: R = pl/A = pl/ ฯr2_x000D_
2ndcopper wire: Rโ = pโlโ/Aโ = pl/(4 ฯr2) = R/4_x000D_
If joined in parallel, (1/Req) = (1/R) + (1/Rโ)_x000D_
= 1/R + 4/R_x000D_
= 5/R_x000D_
Req = R/5
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