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Transformer vs ohm's law

  1. Feb 4, 2007 #1
    According to ohm's law voltage is directly proportional to current that is if voltage get increased current also should get increased but in a transformer if voltage get increased current get decreased.

    so, Is a transformer is obeying ohm's law or not
  2. jcsd
  3. Feb 4, 2007 #2
    You are not applying ohms law to the transformer correctly when stated the way you have. If you apply 100 volts to a 10:1 transformer you will end up with 10 volts out. If you put a 10 ohm resistor on the secondary you will have one ampere passing through the resistor. In an ideal transformer the 100 volt source will be sourcing .1 amps. Increase the primary voltage by a factor of 2 and the secondary voltage will increase by the same. The amps in both windings will increase by a factor of 2 as well. Ohms law has not been violated.
  4. Feb 4, 2007 #3


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    Staff: Mentor

    To put it another way, Ohms law is for determining the behavior of electricity through a load (a resistor). A transformer by itself is not a load.

    We see people make this mistake a lot (that's 3 times in 3 days) and I don't know why...
  5. Feb 4, 2007 #4
    Yep. Remember that Ohm's law only applies for Ohmic devices (which obey Ohm's law and hence named thus).

    (Seriously, I'm not trying to be smart or patronising here.)
  6. Feb 4, 2007 #5


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    Staff Emeritus
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    Gold Member

    You apply Ohms law separately to the primary circuit and to the secondary circuit of a transformer. You do not use Ohms law to learn how the primary induces current in the secondary.
  7. Feb 5, 2007 #6

    Thanks a lot to every body who had taken care for replying this thread.

    I've got some information from your answers.

    Thank you ........:smile:
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