Questions
A material B has twice the specific resistance of A. A circular wire made of B has twice the diameter of a wire made of A. Then for the two wires to have the same resistance, the ratio of lB / lA of their respective lengths must be
detailed solution
Correct option is D
Let the specific resistances, lengths, radii and areas of wires A and B be ρA,lA,rA,AA and ρB,lB,rB,AB respectively.Resistance of A = RA=ρAlAπrA2Resistance of B= RB=ρBlBπrB2According to given question, ρB=2ρA,rB=2rA and RA=RB ThereforeρAlAπrA2=ρBlBπrB2Further, ρAlAπrA2=2ρAlBπ2rA2∴ lBlA=21=2Similar Questions
In an electrical cable there is a single wire of radius 9 mm of copper. Its resistance is 5Ω . The cable is replaced by 6 different insulated copper wires, the radius of each wire is 3 mm . Now the total resistance of the cable will be
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