What is the resistance of a non-ohmic resistor in v-i graph

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SUMMARY

The resistance of a non-ohmic resistor, such as a lamp, is defined as the ratio of voltage (V) to current (I), not the slope of the voltage-current (v-i) graph. In a v-i graph where voltage is on the x-axis, the slope represents the inverse of resistance (1/R), while if current is on the x-axis, the slope equals resistance (R). For non-ohmic resistors, the relationship between V and I is nonlinear, meaning the ratio V/I does not equate to the slope of the curve. Impedance (Z) is defined as the derivative of voltage with respect to current (dV/dI) and varies based on the components in the circuit.

PREREQUISITES
  • Understanding of Ohm's Law (V = IR)
  • Familiarity with voltage-current (v-i) graphs
  • Knowledge of impedance and its distinction from resistance
  • Basic concepts of circuit analysis involving linear and nonlinear components
NEXT STEPS
  • Research the differences between impedance and resistance in AC and DC circuits
  • Learn about the characteristics of non-ohmic resistors and their v-i behavior
  • Study the application of calculus in circuit analysis, particularly derivatives in relation to voltage and current
  • Explore the effects of reactive components (inductors and capacitors) on impedance in circuits
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Electrical engineers, electronics students, and anyone involved in circuit design and analysis, particularly those working with non-linear components and impedance calculations.

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What is the resistance of a non-ohmic resistor (lamp) in v-i graph given a voltage?
I thought it would be the gradiant for specific voltages.
But apparentlly it is the ratio of the specific voltage/current which makes sense too.
So what is the correct out of the two?
 
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is voltage on the x-axis and current on the y or the other way around .
if voltage is on the x-axis then the slope of that line would be 1/R
if current is on the x-axis then the slope of that line would be R
using I=V/R
 
Last edited:
For a non-ohmic resistor, the ratio V/I is not necessarily the same as the slope of the curve.

If y = x^2, then x = 3 implies y = 9 so y/x = 3, but dy/dx = 6.

Since resistance is defined via Ohm's law the resistance is the ratio, not the slope.
 
dulrich said:
For a non-ohmic resistor, the ratio V/I is not necessarily the same as the slope of the curve.

If y = x^2, then x = 3 implies y = 9 so y/x = 3, but dy/dx = 6.

Since resistance is defined via Ohm's law the resistance is the ratio, not the slope.

I'm not sure I'm understanding which one you are promoting, but the impedance is definitely the slope of the line:

Z = dV/dI

This is used all the time in circuit analysis.
 
I was arguing on the opposite side. I'm not an expert on electronics, so I defer to you. Is there a difference between impedance and resistance? I was thinking in terms of DC voltage.
 
dulrich said:
I was arguing on the opposite side. I'm not an expert on electronics, so I defer to you. Is there a difference between impedance and resistance? I was thinking in terms of DC voltage.

If all the components are resistors, then impedance = resistance.

If some of the components are non-liinear (like diodes for example), then impedance = Z = dV/dI, and it is still real.

If some of the coponents are reactive (inductors and capacitors), then you get a complex Z = dV/dI, with real and imaginary (in-phase and quadrature-phase) components.
 

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