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Hi Al,
Interesting argument, but again your logic is flawed, you are making an 'assumption' that you know the value of the resistor beforehand.!
You cannot base a premiss on an assumption.
If I gave you an umarked resistor for 'your experiment', how would you determine the resistors value using only a current meter.?, you cannot.
If I used your assumtion process, I could say, if you know the value of the resistor, I know the diode is a 1N4148 for example,
From the datasheet for the 1N4148, I could tell the resistance of the diode at a know current.
You are taking a simple equation, derived from Ohms law and trying to disprove it, why.?
The 'mathematical' equation by definition must be true for R = V/I , if you know the values of V and I
For the resistor that follows Ohm's Law VR=I*R and once we know the resistance R by ONE SINGLE MEASUREMENT we can then calculate VR for NEW CURRENTS 'I' using OHMS LAW.
For the resistor, you can calculate a new VR for any I after taking just ONE SINGLE MEASUREMENT of both V and I.
Thus, with the resistor Ohm's Law allows us to calculate something that
YOU CAN NOT CALCULATE FOR THE DIODE KNOWING THE SAME INFORMATION.
Here is another way of looking at it... If you had to store the formula for a resistor in the computer, it would take three variables and you could calculate V for ANY resistor
for any I by simply replacing R with the resistors value. With the diode, you need to take up more disk space because the formula is much more complex involving logarithms. Thus, the entropy of the two systems is MUCH DIFFERENT where the diodes is much larger than the resistors. Thus, more information is required to completely characterize the diode than the resistor.
Now if the diode follows Ohm's Law, how can the equation for the voltage contain another completely different term? Simple: it does not follow Ohm's Law.
MrAl,
That is what I am avering is not true. Ohm's Law is NOT V=IR . V=IR or V=IZ is the resistance formula or impedance formula, not Ohm's law. Ohm's law is a property of a material (current vs voltage linearity), not a method of calculation or definition of resistance or impedance of a component or circuit. Saying that V=IR is Ohm's law is propagating an entrenched misnomer.
Isn't that two measurements? Anyway it all boils down to linearity.
Well, you can calculate the diode current vs voltage using the diode equation. It won't be linear, and have the Ohm's law property, but it can be done.
The ease of calculation using a computer has nothing to do with Ohm's law. It is a property of resistance linearity and has nothing to do with how something is calculated.
That's right. The current vs. voltage plot of a diode proves it is non ohmic, because its plot is not straight line.
Ratchit
Ratchit, you've taken my statements out of context and used them to argue
against some point which my statements never intended in the first place.
In fact you take one statement, disagree with it, then agree later in your own
post! Doesnt make sense.