1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ohm's Law validity

  1. Nov 2, 2014 #1
    1. The problem statement, all variables and given/known data

    When would Ohm's law not be valid. Does Ohm's law only work with specific resistors, i.e. when R = 25 ohms? As the current flows and the resistor heats up does resistance change?

    2. Relevant equations

    V = IR

    3. The attempt at a solution

    I would say that no, Ohm's law is not going to be valid all the time. There are specific materials that are designed to be resistors and can handle a certain amount of current. I've been reading about diodes and I'm not really sure what they are, but I believe they do not hold true to Ohm's law. I also want to say that conductors and transistors do not apply to Ohm's law. From these conclusions, I think that as current flows and the resistor heats up, resistance does change because the resistor is meant to handle a certain work load. As those parameters change, the resistor would probably fail and resistance would lessen.
     
  2. jcsd
  3. Nov 2, 2014 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    If one simply defines resistance as Voltage/Current, then V = I R holds. But, as you clearly point out, for a lot of situations R is not a constant, which takes away the predictive capability of Ohm's law for those situations.

    But even for diodes, light dependent resistors, etc. one can call ##\Delta V / \Delta I## the resistance at a given V, and for (very) small ##\Delta V##.

    Common understanding of Ohm's law includes the silent assumption / implicit condition that R is constant. It is a linear model, a simplification of reality. In practice it holds over many orders of magnitude for the devices we call resistors, but not for all: too much current and they blow up. Then you have ##R=\infty## :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Ohm's Law validity
  1. Ohm law (Replies: 2)

  2. Ohm's Law and power (Replies: 1)

  3. Ohm's Law (Replies: 4)

  4. Ohms law (Replies: 1)

  5. Ohm's law (Replies: 3)

Loading...