MaterialResistivity r(ohm m)Temperaturecoefficientper degree CConductivity s x 107 /WmSilver1.59x10^-8.00616.29Copper1.68x10^-8.00685.95Aluminum2.65x10^-8.004293.77Tungsten5.6x10^-8.00451.79Iron9.71x10^-8.006511.03Platinum10.6x10^-8.0039270.943Manganin48.2x10^-8.0000020.207Lead22x10^-8...0.45Mercury98x10^-8.00090.10Nichrome(Ni,Fe,Cr alloy)100x10^-8.00040.10Constantan49x10^-8...0.20Carbon*(graphite)3-60x10^-5-.0005...Germanium*1-500x10^-3-.05...Silicon*0.1-60...-.07...Glass1-10000x10^9......Quartz(fused)7.5x10^17......Hard rubber1-100x10^13......
According to ohm’s law, the resistance of a
metallic conductor depends on the following:
1. Length of the conducting wire- the longer
the wire, the higher its resistance.
2. Cross-sectional area of the conductor- the
thicker the conductor, the lower the
3. Nature of the conductor- the more free
electrons there are, the lower the resistance.
ρ=resistivity of the conductor
(Ω·m / ohm-meter)
L=length of the wire (m)
A= cross sectional area (m2)
What length of copper wire
will provide a 5.00Ω
resistance if its cross
sectional area is 0.100mm2?
Given that resistivity of a
copper is 1.7x10-8 Ω·m)
1. The heating element of an electric toaster is
typically made of nichrome wire (an alloy of
nickel and chromium). As current passes
through the wires, the wires heat up, thus
toasting the toast. Estimate the overall
resistance of a heating element which is 220
cm long and consists of nichrome wire with a
diameter of 0.56 mm. The resistivity of
nichrome is 110x10-8 Ω•m