So, what exactly, is that tunnel diode's resistance when there is 3mA flowing through it?
In Ohm's Law, three parameters are involved: voltage (U), current (I), and resistance (R). Knowing only one of these parameters makes it impossible to accurately predict the other two.
To determine the resistance of the tunnel diode at a specific conditions (operating mode) with specified current of 3 mA, it is also necessary to know the voltage drop across the diode at that moment. Only with both values (voltage and current) Ohm's Law can be applied to calculate resistance of tunnel diode.
And given that the tunnel diode is a nonlinear component, you cannot assume that the calculated R will remain constant under varying conditions. The calculated R value will be only relevant for the specific operating mode in which it was determined.
[1] For example, in this component there is 3mA flowing trough it. What is the voltage across it? What is its resistance?
To accurately apply Ohm's Law in this scenario, you first need to establish the tunnel diode at the specific operating mode point you wish to test. Once the diode is set to this operating mode point, you can measure the voltage across it and the current flowing through it to calculate the resistance using Ohm's Law.
However, it's important to note that for the same current (3 mA), there may be multiple voltage values across the diode depending on its operating condition. If the diode is in a different operating mode, achieving the same current and voltage would require adjusting the diode's state through a different method. Therefore, the resistance value calculated will only be applicable for the particular operating mode you've established.
This distinguishes non-linear components from linear one, where R is constant, resulting in a unique voltage value for a specific current. However, you can note that Ohm's Law remains applicable in both cases.
Hello there,
This discrepancy about Ohm's Law comes up from time to time on the web. This might be the fifth time or more that I've seen people try to claim that "Ohm's Law" holds for every single situation no matter how obscure.
You probably do not realize it yet, but what the equivalent to what you are saying is that:
c=a/b
is Ohm's Law. That's not a Law, and just because we change the lettering that does not make it what we usually refer to as Ohm's Law either. In fact, Ohm's Law is not a true Law either.
Let me list a few here:
c=a/b
d=g/f
a=b*c
m=diddly/tweedly
r=v/i
Which of those is Ohm's Law?
None of them, not even the last one, because OL involves constant quantities not variable quantities.
To be more succinct, we might write in upper case:
R=V/I
and maybe we can take that to be Ohm's Law because it helps us SOLVE something without any more information. If you need more information about the current or voltage, then what you are implying is something like this:
r=v(t)/i(t)
or even:
r=v(t)/i(x)
and what this tells us is that both 'v' and 'i' are functions that must be defined before we can calculate r.
Like some of the other examples posted by others in this thread but I'll add one more:
y=r*sin(angle)
Now this might look like:
y=R*sin(angle)
but it's not. It's entirely different. The second means we have a constant radius so 'y' will plot out a half circle if we span the angle from 0 to pi. However, the first is not the same as the second because 'r' is a variable also, and that means it could be a function:
y=r(t)*sin(angle)
and notice now we have two independent variables not just one (which was the angle previously).
Now as to the constraints on the formula:
r=v/i
if we constrain 'v' and 'i' to stay within certain limits, we still don't have Ohm's Law. I bring this up because you said that sometimes we can calculate Ohm's Law at a point if we limit the span of the variables.
That's still not Ohm's Law. That's called "Linearization" about a point. We then go about to 'pretend' that it obeys what we refer to as Ohm's Law.
I really like the example of the negative resistance though. That really kicks this thing in the butt. There's no way we can call that Ohm's Law. If we try to say that we can get a negative resistance R with R=V/I we would have to say that one of the variables V or I is negative, as in:
R=-2/3
or:
R=2/(-3)
and this makes little sense also because it does not matter what the polarity is, the resistance is always positive. For example, if we apply +5 volts with a current of 5 amps, R=1 Ohm, but if we apply -5 volts with 5 amps, the resistance is still R=1 Ohm.
It is also noteworthy to mention that 'resistance' is not the same as 'Ohm's Law' just because we use units of "Ohms" for resistance. Ohm's Law and resistance are two different things. We can have a resistive element that does not follow what we call Ohm's Law. This has been demonstrated many times in the past with the diode equation.
In other words, if Ohm's Law holds for diodes just because they exhibit Ohmic behavior about a certain operating point, then why do we need the Diode equation?
The diode equation looks something like this:
id=is*(e^(qv/nkT)-1)
and if we lump some constants and use an approximation based on 'is' always being much smaller than 'id' we can come up with this:
v=log(id)*K (where K is just some of the constants lumped)
and this shows us that the voltage is proportional to the natural log of the current, not proportional to the current. And this is even after using an approximation that makes the expression even simpler than it was originally.
This shows that this:
v=log(id)*K
is certainly not the same as:
V=I*R
they are two different relationships. If we could call the first one as the second one then we might as well say we have one formula:
v=i*r
for everything in the universe. Why not? If we "just have to know more about the current or voltage" (or whatever else) then we can use Ohm's Law to describe anything we want to use it for.
What is the temperature of the sun? It's v=i*r of course.
What is the rotation of the earth around the sun? It's also v=i*r, what else could it be.
What is the quantum state at the second location when we use teleportation to transmit the state to the that second location? Why, it's v=i*r, naturally!
I think this happens because we use formulas regularly without really knowing or remembering the mysteries behind some of them. We all do this at some point. Also, we use the word "Ohms" for resistance and so we can start to believe that everything that has resistance follows Ohm's Law.