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Homework Help: Find the resistance of the coil

  1. Feb 12, 2012 #1
    1. The problem statement, all variables and given/known data
    A water heater consisting of a metal coil that is connected across the terminals of a 24-V power supply is able to heat 270 mL of water from room temperature (20°C) to boiling point in 70 s. What is the resistance of the coil? (When entering units, use ohm for Ω.)

    2. Relevant equations
    R = dV/I

    3. The attempt at a solution
    I am not sure how to approach this one. I think the temperature is throwing me off. I have V so I am trying to find I. I was thinking of using I = dQ/dT since I have the time interval, but finding Q isnt possible unless I am given values for charges. I almost want to use Q = mc*dT but Q here is thermal energy so I'm back to square one.
  2. jcsd
  3. Feb 12, 2012 #2


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    Staff: Mentor

    Your thought about thermal energy looks promising. How much energy is required to heat the given amount of water by the stated amount? If it's done in the stated amount of time, what's the power (watts) involved?
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