7 resistivity

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  • 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......
  • 7 resistivity

    1. 1. 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 resistance. 3. Nature of the conductor- the more free electrons there are, the lower the resistance.
    2. 2. Material Silver Copper Aluminum Tungsten Iron Platinum Carbon* (graphite) Germanium* Glass Quartz (fused) Hard rubber Resistivity R (ohm m) 1.59 1.68 2.65 5.6 9.71 10.6 x10^-8 x10^-8 x10^-8 x10^-8 x10^-8 x10^-8 3-60 x10^-5 1-500 1-10000 x10^-3 x10^9 7.5 x10^17 1-100 x10^13
    3. 3. R=ρL/A R=resistance (Ω/ohms) ρ=resistivity of the conductor (Ω·m / ohm-meter) L=length of the wire (m) A= cross sectional area (m2)
    4. 4. 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)
    5. 5. L= 2.94 x 4 10 m
    6. 6. A platinum wire 1.50mm in diameter conducts a current of 9.00 A. Find the potential difference between two points on the wire 125m apart? (ρ =11.0x10-8 Ω·m) platinum
    7. 7. V=70.0V
    8. 8. 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
    9. 9. R=9.8 Ω

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