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Homework Help: Diameter of a wire with length, resistance and resistivity

  1. Jan 1, 2010 #1
    1. The problem statement, all variables and given/known data
    This question is about the heated front windscreen of a car
    The heater consists of resistance wires which are embedded in the glass

    A) The power of the heater needs to be 180W for a satisfactory demisting
    A car battery of Negligable internal resistance supplies 12V to operate on the heated screen

    Calculate the current required to deliver a power of 180W
    180/12=15A

    Show that the resistance of the heater when operating is about 1ohm
    12/15=0.8 ohms, rounded up=1ohm

    B) the heater consists of 200 wires inside the glass
    These wires are connected in parallel to the 12V supply

    Each of the 200 wires has a length of 0.70m and a resistance R(subscript)p of 160 ohms
    The material of the wire has resistivity p=6.0x10^-7ohmic metres

    Calculate the DIAMETER of the wire

    please people, I don't want the answer, can someone just help me out and give me the equation I need to use? I'm terrible at remembering equations I really need the equation, thanks x
     
  2. jcsd
  3. Jan 1, 2010 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi Elka! Welcome to PF! :smile:

    Resistance = resistivity times length over cross-section area. :wink:
     
  4. Jan 2, 2010 #3
    Thank you Tiny Tim! Thats great! You've helped me pick up 4 marks definately and maybe 5! (past papers homeworks) Thank you so much, you're a lifesaver :D
     
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