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Homework Help: Electrical Wiring - corrosion, cracking and resistance.

  1. Apr 2, 2010 #1
    1. The problem statement, all variables and given/known data
    Been racking my brains over this one and I'm stuck maybe someone here can help me. I'm doing physics through distance education at high school and its very difficult.

    "In house fires the wiring is often cited as the cause of the fire. Often this wiring is partially corroded through or cracked. Explain why this may be a contributing factor in causing the fire by referring to what you have learned about resistance."

    2. Relevant equations
    n/a

    3. The attempt at a solution

    I honestly have no idea at all how the crack or corrosion could cause a change in resistance and lead to a fire. I have learned that the following factors influence resistance:

    1 - length
    2 - type of material
    3 - cross sectional area
    4 - temperature

    As well as this I'm aware of Ohm's law...

    I'm thinking it may have something to do with the temperature but I'm really just pulling ideas from nowhere.

    Any help would be very very much appreciated.

    Thanks
     
  2. jcsd
  3. Apr 2, 2010 #2
    Corrosion would have the effect of changing the material (oxidization?), and thus the resistance of the wire.
    Cracking or crushing or bending the wire, can change its cross section area.
     
  4. Apr 5, 2010 #3
    ahh okay. thanks :D
     
  5. Apr 5, 2010 #4
    To be more precise, both in fact, have the same effect. They reduce the cross-section area of the conducting part of the wire (The oxides that form as a result of corrosion are insulators).

    Use Joule's Law (Power dissipation in a resistor), and the formula for resistance in a wire to find how this effect may cause the wire to ignite.
     
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