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Homework Help: Efficiency of a Transformer

  1. Mar 6, 2010 #1
    1. The problem statement, all variables and given/known data

    The specifications of a transformer for a small appliance read "Input: 110 V, 6.4 W" and "Output: 8.9 V, 270 mA". What is the efficiency of this transformer?

    2. Relevant equations

    P = I * V

    V = I * R

    3. The attempt at a solution

    6.4 W / (8.9*(270*.001)) ---> I think this is wrong

    I am just not sure how the voltage drop of the transformer would affect the power output...
  2. jcsd
  3. Mar 6, 2010 #2
    Your reasoning is absolutely correct, voltage drop theoretically shouldn't affect the power output, but in theory we assume that there is no losses, no heat generated etc.
    Thus when such a question pops up (power out)*100/(power in ) will give you the efficiency.
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