A resistor or resistance is considered Ohmic if it has a linear IV plot. A proportional increase in amperage for a proportional increase in voltage.
Ohm's law doesnt break but if the resistance changes at a given applied voltage then it may not be ohmic or in other words it is nonlinear.
Morning Kiss,Ohms law states that the relationship between voltage and current is a constant.
Maybe thats not what I seemed to say but it ks exactly what I meant.hi,
You are incorrectly stating Ohms law.
Ohms law says the Current thru a conductor is proportional to the applied voltage and inversely proportional to the conductors resistance.
I = V/R.
Linearity does not come into Ohms law.
So as the tungsten filament heats up its resistance increases, so Ohms law still applies.
Semiconductors are usually considered non linear devices, but these also obey Ohms law for any given value of Current and Voltage at that instant.
E
Ohm's Law is a linear equation (https://www.google.com/?gws_rd=ssl#q=linear+equations). As such it assumes an "instantaneous" and constant set of values for any two of the three variables and, as a result, by definition gives a result that is also a constant.By the way I care about ohmic or non ohmic because I want to know whether a resistance measurement will be a reasonably accurate predictor of loaded circuit performancs. Or whether voltage drops on the loaded circuit must be used. ...
At stall, a DC motor can be considered a simple, fixed resistive circuit (at least after the initial "in-rush" current has stabilized).I measured resistance on a DC motor commutator , different segments and the resistances were very low so maybe the most resistance comes from "CEMF" if you call that resistance. ...
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Semiconductors are usually considered non linear devices, but these also obey Ohms law for any given value of Current and Voltage at that instant.
1. Ohm's Law deals with the relationship between voltage and current in an ideal conductor. This relationship states that:
The potential difference (voltage) across an ideal conductor is proportional to the current through it.
The constant of proportionality is called the "resistance", R.
Ohm's Law is given by:
where V is the potential difference between two points which include a resistance R. I is the current flowing through the resistance. For biological work, it is often preferable to use the conductance, g = 1/R; In this form Ohm's Law is:
V = I R
2. Material that obeys Ohm's Law is called "ohmic" or "linear" because the potential difference across it varies linearly with the current.
I = g V
Ohms Law and Materials Properties
**broken link removed** In this subchapter we will give an outline of how to progress from the simple version of Ohms "Law", which is a kind of "electrical" definition for a black box, to a formulation of the same law from a materials point of view employing (almost) first principles.
**broken link removed** In other words: The electrical engineering point of view is: If a "black box" exhibits a linear relation between the (dc) current I flowing through it and the voltage U applied to it, it is an ohmic resistor.
**broken link removed** The (extreme) Materials Science point of view is: Tell me what kind of material is in the black box, and I tell you:
- If it is an ohmic resistor, i.e. if the current relates linearly to the voltage for reasonable voltages and both polarities; and
- What its (specific) resistance will be, including its temperature dependence.
- And everything else of interest.
True enough, eric, but the equation is linear and as such, in a single use, is incapable of rendering anything but a linear solution.Also Ohms Law, as defined does not mention linearity.
Hi,
There are really two different interpretations of what is "ohmic" and what is not. I will explain both and show a clear example of this.
Ohm's Law is the first, and can be stated as:
E=I*R
but in this strictest sense R must be a constant. That's right, R must be a constant or it does not hold. If R is allowed to vary, then there might as well be no law at all. In this way Ohm's Law is sometimes said to be "self fulfilling".
The other 'view' is that anything that dissipates heat can be called "ohmic" which comes from the expression:
P=I^2*R
and this separates it from those elements that store energy which do not dissipate heat, but here R does not really need to be constant because even if it is not there is still power dissipated.
Now how can we be sure there are two different interpretations? All we need is a single device that can be interpreted using both definitions so we can see each in it's own light. Luckily we have such a device and is quite common: the ordinary silicon diode. Looking at this device we can see the differences and similarities between the two definitions.
We can separate the physical diode into two separate parts:
1. The ohmic contact part, which follows Ohm's Law quite closely.
2. The 'diode' part which is non linear for voltage and current.
The ohmic part follows E=I*R, while the base diode part follows an exponential.
The ohmic part follows Ohm's Law, while the exponential does not. So we can see the difference because of the different curves.
However, both parts generate heat. For the ohmic part we have:
Po=I^2*R
and for the exponential part we have:
Pe=I^2*r(v)
or:
Pe=i^2*r(i)
and Po and Pe are both real powers there is no imaginary part here. The difference is that Po can be calculated knowing only the current and a fixed constant, R, while for Pe the resistance changes with either the current or voltage (or both). This makes the two functions very different.
Why think about it as two different ideas, why not just one with a variable resistance?
This is like asking why have resistors and transistors, why not just have transistors since we can use them as resistors if we bias them to our liking.
I'll post the diode curve if anyone is interested.
True enough, eric, but the equation is linear and as such, in a single use, is incapable of rendering anything but a linear solution.
I believe I understand. A diode's conductivity changes depending on the magnitude and polarity of the applied voltage. My meter has a diode check function, I have heard .7V may be needed to "forward bias" it into a conducting state.
Some diodes, Zener? or Avalanche, will break down into a conducting state for a short time.
What is P? Power, in what terms exactly / how is it related to electrical units?
It seems to be a description of a measurement of work? I am tired :-(
Watts would be a measurement of the rate at which work is being done, by comparison?
Volts, of potential difference in electrical Charge,
Charge measured in coulombs.
And amps = movement of charge per second.
What do you call V/I?...No matter what you call V = I*R, circuits will still get designed and analyzed, and science will still progress.
What do you call V/I?
What do you call dv/di?
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