# Ohms Law Clarification.

Discussion in 'General Electronics Chat' started by kramer, Nov 22, 2012.

1. ### kramer Thread Starter New Member

Nov 20, 2012
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In response to TriggerNum5 & Ratch...

You're both correct, kind of. I believe you are getting confused between RESISTANCE and RESISTIVITY.

It is actually Resistivity that you are referring to, which is a material property and therefore defines an Ohmic material. Resistivity is a function, but not of V or I, so is therefore independent from them.

Resistivity (K), or rather Conductivity (1/K), is a ratio of the electric field (Newtons per Coulomb) and the current density (J, or Amps per Square Metre). This value is determined by the number of free charge carriers (i.e; electrons) a material has. For copper, this number is high, as one would expect as it is a great conductor. For an insulator, such as Teflon, the number of charge carriers is low. For a semiconductor, the number of charge carriers is determined by the materials exposure to an external electric field.

Getting down into the real physics of it, it is more related to component design (ie, FETs).

2. ### tshuck Well-Known Member

Oct 18, 2012
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Not quite true

Don't forget about doping... also, what happens when light hits an intrinsic semiconductor?

3. ### Wendy Moderator

Mar 24, 2008
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We use the Physics forum for those areas where are not basic electronics. This is as basic as it gets, and I have therefore moved to a more appropriate forum.

It is interesting to not that Ratch was evicted quite a few years ago for pushing his own theories to beginners, who need to learn the basics to simply pass their courses. It is important to note that while you need not agree with conventional theory, people starting out must learn the text book before they can diverge into other ideas of thought.

Given the two members (it has been many years since we've seen TriggerNum5) I'm not sure what prompted this thread, but it does not matter. Ohms Law is always open for discussion. It is one of the concepts you must get down before continuing your education.

As tshuck mentions though, it only applies to linear systems.