Resistance in case of non Ohmic current voltage relation.

In summary, the non Ohmic relation of current and voltage is I=α(exp(eV/kT)-1). Where α,K,T,e are constant. The incremental resistance is found by using a derivative (dV/dI) which is in units of ohms.
  • #1
Mitadru Banik
11
0
A non Ohmic relation of current and voltage is I=α(exp(eV/kT)-1). Where α,K,T,e are constant. What will be the incremental resistance?

My question is if it don't follow the Ohmic equation then how it possible to find the resistance?
 
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  • #2
Mitadru Banik said:
A non Ohmic relation of current and voltage is I=α(exp(eV/kT)-1). Where α,K,T,e are constant. What will be the incremental resistance?

My question is if it don't follow the Ohmic equation then how it possible to find the resistance?

Incremental resistance refers to small signal resistance. This means that when you take a non-linear load line like the one described by your equation, and vary your position along that line very small by changing the voltage or current respectively small, you will be operating along an -approximate- linear region, since the tangent along this curve at any point is a straight line, which will be an ohmic relation in the sense that it is linearized on this small increment.

Incremental should give you the clue to use a derivative (dV/dI) which is in units of ohms.
 
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  • #3
Ok understand it but however it never violets the relation V=IR.
 
  • #4
Mitadru Banik said:
Ok understand it but however it never violets the relation V=IR.
When speaking of incremental resistance, written as small r, then Ohms Law is written v=i·r
to distinguish 'r' from the DC or large signal resistance seen in V=I·R

Example: If you apply, say, 10 volts DC to an nonlinear resistor and a current flows of 1 ampere, you conclude that that resistor, at 10 volts, seems like a 10 ohm resistor. However, if you increase that 10V to 10.1V and find the current increases to 1.05A, you can say that for small changes near 10V, that resistor appears as a 2 ohm resistor because ∆V/ ∆I = 2Ω.

So at the 10V operating point the resistor simultaneously has two values of resistance, R=10Ω and r=2Ω.
 
  • #5
Mitadru Banik said:
Ok understand it but however it never violets the relation V=IR.

Don't worry about that. There is no violation.
It may be better if you don't feel that the 'Resistance' actually has to mean anything, other than V/I. If you don't insist that there must be some physical significance then there is no problem. Likewise, the 'small signal' resistance (ΔV/ΔI) needs to be no more than what it says on the tin.
There are enough really important things to get in a stew about so why worry about what something really 'means'?
One of the first things we have to get over in 'electrics' is to realize that descriptions of Resistance like "It's how hard you need to push electrons through a circuit" are no use to anyone. Resistance is just a RATIO - period.
 
  • #6
Thanks to all of u...
 

1. What is the definition of non Ohmic current voltage relation?

Non Ohmic current voltage relation, also known as non-linear current voltage relation, refers to the relationship between the current and voltage in a circuit, where the resistance varies as the applied voltage changes. In contrast to Ohmic materials, which have a constant resistance regardless of voltage, non Ohmic materials have a resistance that changes with voltage.

2. What causes non Ohmic current voltage relation?

Non Ohmic current voltage relation is caused by various factors, such as temperature, composition, and structure of the material. These factors can affect the movement of electrons, resulting in a change in resistance as voltage is applied.

3. How does resistance behave in non Ohmic materials?

In non Ohmic materials, resistance increases as voltage increases. This is because as voltage increases, the flow of electrons through the material becomes more difficult, leading to an increase in resistance.

4. What are some examples of non Ohmic materials?

Some common examples of non Ohmic materials include semiconductors, thermistors, and gas discharge tubes. These materials have a varying resistance with changes in voltage, making them useful in electronic devices such as sensors and amplifiers.

5. How is resistance measured in non Ohmic materials?

In order to measure resistance in non Ohmic materials, a voltage-current graph can be plotted and the slope of the line can be used to determine the resistance. Alternatively, a multimeter can be used to directly measure the resistance at different voltage levels.

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