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Homework Help: Uncertain of 2 problems (answers given, but don't know solution-help!)

  1. May 2, 2008 #1
    Uncertain of 2 problems (answers given, but don't know solution--help!)

    1. An electric iron draws 9 amperes from a 120-volt line. The iron's mass is 0.8 kilograms, and it is originally at 20 degrees Celsius. 40% of the heat is lost to the room by radiation. What will the temperature of the iron be 2.0 minutes after it's connected. Assume constant resistance.
    Answer is 231 degrees Celsius (note that 60% of power input goes to heating the iron)

    2. A drop of water in a fog has a net charge of 200 electrons. What is the radius of the drop if it is suspended motionless on a day when the earth's electric field is 300 volts/meter?
    Answer is radius = 6.16 x 10^-7 meters; hint: electric force must balance weight of drop

    Thank you very much!
  2. jcsd
  3. May 2, 2008 #2

    Doc Al

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    Staff: Mentor

    Hint for 1: Calculate the electrical energy consumed by the iron in 2 minutes.
    Hint for 2: Find the mass of the water drop.
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