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Homework Help: I am new here, this is more of a conceptual confirmation than mathemab

  1. Apr 30, 2014 #1
    When a wire resists an electrical current it produces heat energy. But how efficient is this transfer? If the electrical Power is 20watts is the heating power 20watts? (ignoring all other inefficiencies, just the conversion from Electrical to Heat)

    I'm thinking since a circuit requires electrons to complete the circuit in order to have a current, the Powers won't be equal because some energy will remain within the electrons to keep them in movement.
  2. jcsd
  3. Apr 30, 2014 #2


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    The power loss is given by the formula: ##P=I^2R##. Is this what you are looking for?
  4. Apr 30, 2014 #3
    The electrons in the circuit don't quite work in the way that your intuition would expect, they don't move very fast at all in a circuit. It is actually an electromagnetic wave inside a wire that transfers "electricity".
  5. Apr 30, 2014 #4
    I should probably explain further, I've done a school experiment converting electrical energy to heat. P=VI was used to find the electric power going through the Ohmic heating coil, and got an answer of 30 watts. It was used to heat 0.2kg of water and the equation Q/t = m×c×T/t was used to find the Heating Power which gave an answer of 20 watts. I was wondering if the lower answer is only due to inefficiencies of the experiment or that not 100% of the power is converted and some remains in the heating element as electrical energy.
    Last edited: Apr 30, 2014
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