ANSWERS: 1
  • The conductivity of copper is about 60MS/m S is the unit of conductance: Siemens and is 1/ohm. This means a cube of copper of side 1m has a resistance of 1/60MS = 16.7 nano ohms Stretch this out to 2.5 m long and it will have 2.5 times the resistance (more stuff to tunnel through). So that's 41.7 nano ohms. Squash the block so its only 1mm high and it will have 1000 times the resistance, as the "pipe" for the electrons is 1000 times smaller, Squash it the other way to 1mm so that it is now a square wire of length 2.5m and cross section of 1 square mm and it has a resistance 1000 times 1000 greater = 41.7 milliohms. A round copper wire of 1.5mm in diameter has a crosssectional area of pi * (1.5/2)^2 = 1.767 mm^2 which is a little bigger than my square wire, so the resistance will be a little less: 41.7/1.767 = 23.6 milliohms

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