1.

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

Answer»

<PR/5



1st copper wire: R = PL/A = pl/ πr2
2ndcopper wire: R’ = p’L’/A’ = pl/(4 πr2) = R/4
If JOINED in parallel, (1/Req) = (1/R) + (1/R’)
= 1/R + 4/R
= 5/R
Req = R/5



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