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Current and Voltage in a transformer

  1. Apr 12, 2012 #1
    1. The problem statement, all variables and given/known data

    The primary coil in a transformer has a power of 100W. The flux through a single loop in the primary is changing at a rate of 25 Wb/s. The primary has 100 loops and the secondary has 500 loops. Assuming a perfect transformer (no losses), determine the current and voltage in both the primary and secondary.

    2. Relevant equations



    3. The attempt at a solution



    I have no knowledge of an equation/relationship between Wb/s and the other variables in this problems nor can I find one. Please Help.
  2. jcsd
  3. Apr 12, 2012 #2


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    Staff: Mentor

    A hint can be found in the units: A Weber (Wb) has the equivalent units of V*s (that is, one Weber is a Volt-second).

    Given the rate of change 25 Wb/s for a single loop, what's the voltage on the primary?
  4. Apr 12, 2012 #3
    So it would be 25W then?
  5. Apr 12, 2012 #4
    i mean 2500W since its per loop
  6. Apr 12, 2012 #5


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    Staff: Mentor

    Sorry, I don't understand your response. Your given information states that there is 100W associated with the primary. What's this 2500W you're proposing? Or do you mean 2500V? That would be a reasonable value :smile:

    So, if the voltage on the primary is 2500V, what's the current?
  7. Apr 12, 2012 #6
    Sorry, I did mean 2500V.

    So to find the current I would use


    which would mean that the current would have to equal 1/25 A
  8. Apr 12, 2012 #7


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    Staff: Mentor

    Yes. Now, how will you find the secondary voltage and current?
  9. Apr 12, 2012 #8



    I2=1/125 A

    Is that right?
  10. Apr 12, 2012 #9


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    Staff: Mentor

    Your results look good.
  11. Apr 12, 2012 #10
    Thanks for the help! I really appreciate it
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