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question about ohm's law

Discussion in 'General Electronics Discussion' started by Chengjun Li, Apr 5, 2015.

  1. Chengjun Li

    Chengjun Li

    84
    7
    Oct 21, 2014
    Hi,

    About Ohm's law, wikipedia has the following statement
    “Materials and components that obey Ohm's law are described as "ohmic" which means they produce the same value for resistance (R = V/I) regardless of the value of V or I which is applied and whether the applied voltage or current is DC (direct current) of either positive or negative polarity or AC”

    We also know that resistance of a resistor is a function of temperature. For example, Jameco 100 Ohm resistor has a temperature coefficient of 350ppm.

    My question is at higher voltage, the heat generated is larger due to P=V2/R, so the partial temperature is higher, then the resistance should change to smaller value, which is conflict with above statement of Ohm's law. Could anyone give me some clue of this problem?

    Thanks.
     
    Last edited by a moderator: Apr 5, 2015
  2. ramussons

    ramussons

    342
    61
    Jun 10, 2014
    The blue statement is valid on a condition that all other parameters are constant - temperature, pressure, frequency, ... The only variables are the Voltage / Current.
     
    davenn likes this.
  3. alex Chiu

    alex Chiu

    14
    3
    Apr 1, 2015
    Ohm Law still value.

    P=VI, =
    If R = Constant, Higher V, higher I, however, when consider heat, R reduce, I reduce,
     
  4. davenn

    davenn Moderator

    13,347
    1,774
    Sep 5, 2009
    Great response Ramussons .... spot on :)


    Dave
     
  5. Colin Mitchell

    Colin Mitchell

    1,418
    314
    Aug 31, 2014
    then the resistance should change to smaller value

    should be

    then the resistance should change to higher value
     
  6. Ratch

    Ratch

    1,044
    308
    Mar 10, 2013
    You should read this link http://www.electro-tech-online.com/threads/ohms-law.430/page-2 starting with my contribution on post #22. Then we can discuss it further.

    Ratch
     
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