1. Resistance and resistivity, again. A conductor of radius r, length l and resi

Question

1. Resistance and resistivity, again. A conductor of radius r, length l and resistivity has resistance R. It is melted down and formed into a new conductor, also cylindrical, with one half the length of the original conductor. The resistance of the new conductor is -is my answer correct R/4?

2. Most telephone cables are made of copper wire of either 24 or 26 gauge. If the resistance of 24-gauge wire is 100 /mile and the resistance of 26- gauge wire is 400 /mile, what is the ratio of the diameter of 26-gauge wire to that of 24-gauge wire? is my answer correct 2?

Explanation / Answer

part 1 ) if we are not changng area of conductor

then R = pL/A

we are making length half of original

=> new resistance = R/2

if we are changing area also

then we have not sufficient data

part 2) R = pL/A

=> R2/R1 = A1/A2 = D1/D2

=> D26/D24 = R24/R26 = 100/400 = 1/4 = 0.25

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