16th June 2009 10:05 PM
By saying that two variables are directly proportional, it is saying that the two variables have a positive, linear relationship. Just as Hooke's Law approximates that the extension of a material is directly proportional to the force applied to it, which is not true for non-hookean materials, Ohm's law approximates that voltage is directly proportional to resistance, which is not true for non-ohmic components.
V = IR and variants are used to calculate V, I, or R from a single set of data; proportionality refers to a continuous function.
What is really being stated is that V(x) = IR(x) for a point x. This implies that current, I, is a constant, which we know is not necessarily the case.
Last edited by giftiger_wunsch; 16th June 2009 at 10:13 PM.
16th June 2009 10:11 PM
Ohm's law in not an approximation. It describes the exact relationship for voltage, current and resisitance and is summed by the V=IR equation, just like the famous E=MC^2 relationsip sums up another famous law. Ohm's law is true for all materials, although the law is not material dependent.
Show me a material that doesn't exhibit continuity.
proportionality refers to a continuous function
16th June 2009 10:44 PM
Look Georg Simon Ohm: The Discovery of Ohm's Law
The relation V / I = R even holds also for non-ohmic devices
, but then the resistance R depends on V and is no longer a constant
I guess if you want to go around denying the laws of physics, then nobody can stop you. [ET: REMOVED SENTENCE]
The equation I = V/R is known as "Ohm’s Law".
Last edited by The Moderation Team; 17th June 2009 at 01:51 AM.
Reason: Insulting other members
16th June 2009 10:48 PM
Clearly we're not going to come to an agreement, so I'm just going to leave it at that.
[ET: REMOVED SENTENCE]
Last edited by The Moderation Team; 17th June 2009 at 01:52 AM.
Reason: Removed retaliation.
16th June 2009 10:55 PM
Last edited by The Moderation Team; 17th June 2009 at 01:55 AM.
Reason: Removed insult and infraction given.
16th June 2009 11:22 PM
Been havin a look at your discussion.I'm a newbie too.Have a look at this site.
Ohm's law calculation calculator calculate magic triangle equation tip online voltage volts resitor resistance amps amperes audio engineering - sengpielaudio Sengpiel Berlin Seems you are both right,but pretty tight fitting to your ideas.S'pose the key word is "Non-Ohmic" components.Looks like others have sorted this out before.They have defined deals as non compliant with a very sound law.Ohms law is a very powerful tool,and if we forget our laws and "Rules of Thumb",we also dispense with our first port of call as far as any diagnostics are concerned.My two cents.
16th June 2009 11:41 PM
That's a mis-statement. Ohm's law holds for non-ohmic materials. I refer you again to this: Georg Simon Ohm: The Discovery of Ohm's Law
This is important. Later in your technical career, you'll have to understand concepts like Small-Signal Resistance. That concept demands that ohm's law holds even for non-linerar resistance materials, aka so called non-ohmic.
Last edited by BrownOut; 16th June 2009 at 11:42 PM.
17th June 2009 12:07 AM
This is from your link above."As stated above, this work included “Ohm’s Law” theory: The relationship of a current passing through most materials is directly proportional to the potential difference applied across the material."
Not out for a stouche, but have an open mind.Don't know whether "most" refers to what you guys were talkin about but "most" doesn't include everything.I'll keep it in mind as I further my career, and leave well enough alone for now. Thanks for the tip.
Regards tim from oz.
17th June 2009 12:11 AM
As I already said; that's a mis-statement. Ohm's law works for all materials. The law relates physical quantities, and is not dependent on material.
The author made a nice calculator applet, but he doesn't really understand the law.
Last edited by BrownOut; 17th June 2009 at 12:11 AM.
17th June 2009 12:15 AM
me either.Just as well only lost two cents.
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