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Voltage and current relation difference between Ohm's law and Power

Discussion in 'General Electronics Discussion' started by bunny, Nov 4, 2015.

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  1. bunny

    bunny

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    Nov 4, 2015
    Hi I am new to this forum According to Ohms law, at constant temperature voltage is directly proportonal to current.
    But when we come to power formula p=vi which means that V is inversly proportional to I. How can we justify this?
    Thanks to all in advance.
     
    Last edited by a moderator: Nov 4, 2015
  2. garublador

    garublador

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    Oct 14, 2014
    Because resistance and power aren't the same thing.
     
  3. bunny

    bunny

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    Nov 4, 2015
    Yar i know that both are not same but they relate same things no? and that to a law must be satisfied for all the things. We know that ohms law is valid only for ohmic conductors but power is same formula no?
     
    Last edited by a moderator: Nov 4, 2015
  4. garublador

    garublador

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    Oct 14, 2014
    I'm not sure I understand the question. Here's an image that shows all of the different ways to relate power, voltage, current and resistance:

    [​IMG]

    What do you believe isn't able to be justified?
     
    hevans1944 and Martaine2005 like this.
  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    No, it doesn't. There is nothing to justify because your statement is incorrect.

    For a constant resistance, voltage is directly proportional to current.
    For a constant power, voltage is inversely proportional to current.

    ak
     
    Last edited: Nov 4, 2015
  6. duke37

    duke37

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    Jan 9, 2011
    To go one step further, P= V*V/R and P=I*I*R.
    These can be derived from Ohms law by substitution.
     
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    What do you mean justify?
    Adam
     
  8. GPG

    GPG

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    Sep 18, 2015
    Marshall Givens?
     
  9. Ratch

    Ratch

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    Mar 10, 2013
    First of all, Ohm's law is not V=I*R, and all its variations. Regardless of what predominates the electrical literature, a good physics book will tell you that Ohm's law is an electrical property of a material, specifically its electrical linearity. I can provide documentation for that statement if necessary.

    So V=I*R is correct, but it is not Ohm's law. It is a definition. R is defined by the amount of current present at a specific voltage (R=V/I). Voltage is the electrical energy density of the charge (joules/coulomb). If V volts are lost to move Q coulombs of charge, then the energy expended is E=V*Q. Power is rate of energy and current is rate of charge. Dividing both sides of E=V*Q by t gives P=V*I.

    Ratch
     
    Last edited: Nov 18, 2015
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