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Resistance in case of non Ohmic current voltage relation. 
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#1
Mar2912, 10:35 AM

P: 11

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? 


#2
Mar2912, 10:59 AM

P: 834

Incremental should give you the clue to use a derivative (dV/dI) which is in units of ohms. 


#3
Mar3012, 06:45 AM

P: 11

Ok understand it but however it never violets the relation V=IR.



#4
Mar3012, 07:23 AM

HW Helper
Thanks
P: 5,141

Resistance in case of non Ohmic current voltage relation.
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
Mar3012, 12:00 PM

Sci Advisor
PF Gold
P: 11,908

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 realise 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
Mar3112, 02:36 AM

P: 11

Thanks to all of u......



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