- 24th October 2006, 10:06 #1

- Join Date
- Aug 2006
- Posts
- 9
- Helped
- 2 / 2
- Points
- 1,216
- Level
- 7

## limitations of ohms law

Can Ohm's law be applied to liquids?

Also plz explain why conductors obey ohms'law??

- 24th October 2006, 10:06

- 24th October 2006, 12:40 #2

- Join Date
- Jul 2006
- Posts
- 109
- Helped
- 10 / 10
- Points
- 1,873
- Level
- 10

## limitation of ohms law

E = IR

#/A = mX/s -- pressure (pounds per area) = velocity (m/s) * resistance (X)

Now solve for X:

s#/A = mX

s#/V = X

Now, does resistance equate with s#/V ?

time(weight)/volume

Hmm...?

What's a pound-second?

You've asked a good question. I wish I had a definite answer. Maybe someone else is more knowledgeable.

I do know that ohm's law is valid in mechanics, but it'd seem we're talking about hydraulics, yes? I'd bet it holds.

Incidentally, look at http://www.posc.org/Epicentre.2_2/Da...tity_type.html

Maybe it holds some answers.

Added after 12 minutes:

Somethng else, just mindless wandering...

Let's say you're at the end of a hall crowded with people.

Ohm's law says I=E/R.

In other words, would your velocity travelling down the hall be proportional to your Force (mass * acceleration) divided by the number of people in your path? It'd seem to me that'd you'd be able to run very fast (high I) were people not in your way. Likewise, it'd seem that the more your mass or the more your accelleration, the more your chances of getting down the hall. Whereas, the more people you encounter the less your chances.

Now make yourself a drop of liquid.

Yeah, I'd bet it holds.

- 24th October 2006, 20:17 #3
## limitation of ohms law

Well, I think, ohm law states no where the state of matter it is applicable to. I mean when you say resisivity or resistance , in no way you are saying that it must be solid in nature. ofcourse Ohm's law should be valid for liquids as well as for gases. for a given configration of a liquid on gas container the current will increase as you increase the voltage..

- 24th October 2006, 21:14 #4

- Join Date
- Feb 2002
- Location
- USA
- Posts
- 1,371
- Helped
- 389 / 389
- Points
- 17,055
- Level
- 31

## limitatons of ohm,s law

Ohm's Law was derived from observation of physical electrical circuits. Although Georg Simon Ohm was educated as a mathematician, Ohm's Law was NOT a mathematically derived theory.

Ohm spent a lot of time in a laboratory gathering experimental data. The relationship between current and voltage across a resistor was something he documented in extensive tables of data he collected. He never answered the question about WHY it was true, only that it was observed fact.

If you apply Ohm's Law outside of his field of observation, you do so at your own risk. Although there are analogies in hydraulics and other physical dynamics, the basic 'Law' is only a statement of observed electrical behavior. The analogy in fluid systems begins to break down when you take such things as flow turbulence and fluid viscosity into account. The closest analogy that works is heat conduction. You can interchange the terms in Fourier's heat conduction equation almost directly with Ohm's Law.

Why Ohm's Law is true involves understanding voltage (potential), current, and resistance at the atomic level. That's more than can be written in a brief forum post.

- 24th October 2006, 21:14

- 24th October 2006, 21:25 #5

- Join Date
- Dec 2005
- Location
- Trinidad and Tobago
- Posts
- 19
- Helped
- 0 / 0
- Points
- 1,366
- Level
- 8

## ohm law limitation

The conduction in liquids is normally due to the movement of ions, unlike solids where it is electrons doing the work.

So as ions get used up in tranfering charge and they have limited mobility I would say that Ohm's law would only not normally be obeyed except when the current is very small.

- 24th October 2006, 21:54 #6

- Join Date
- Oct 2006
- Posts
- 107
- Helped
- 11 / 11
- Points
- 4,173
- Level
- 15

## +limitations of ohms law

V=I*R

if I = water pressure for square centimeter

and R = water pipe area in square centimeter

then V = liquid total pressure = I*R

Of course this is only liquid illustration to Ohm's law

- 24th October 2006, 22:13 #7

- Join Date
- Jul 2002
- Location
- Middle Earth
- Posts
- 4,632
- Helped
- 479 / 479
- Points
- 37,801
- Level
- 47

## state the limitation of ohms law

Even in semiconductors there is carrier velocity saturation which makes Ohm's law not work for high currents.

- 25th October 2006, 19:02 #8

- Join Date
- Aug 2006
- Posts
- 155
- Helped
- 5 / 5
- Points
- 1,958
- Level
- 10

## limitation of ohm;s law

limitation of ohms law is that the physical condition has to stay constant like length, temperature resistivity .... in the case of a conductor..... i am actually dont have any idea about liquid being ohmic conductor or not.....

- 25th October 2006, 21:12 #9

- Join Date
- Jul 2002
- Location
- Middle Earth
- Posts
- 4,632
- Helped
- 479 / 479
- Points
- 37,801
- Level
- 47

## what are the limitations of ohms law

Originally Posted by**mannnish**

- 15th February 2007, 11:40 #10

- Join Date
- Jan 2007
- Location
- India
- Posts
- 195
- Helped
- 9 / 9
- Points
- 2,347
- Level
- 11

## what are the limitations of ohms law

ohms law may not be useful for liquids as temperature of the total liquid amy not be constant......