Non-Ohmic Materials: Learn About Vanishingly Small Terms

  • Thread starter Thread starter snatchingthepi
  • Start date Start date
  • Tags Tags
    Materials
Click For Summary
SUMMARY

This discussion centers on the characteristics of non-Ohmic materials, specifically superconductors and their "vanishingly small" quadratic or cubic terms in the context of Ohm's law, represented as J = σE. Participants highlight that while traditional Ohmic materials exhibit linear conductivity, slight non-linearities can occur under high current densities, particularly due to transient heating effects. Examples include Voltage Dependent Resistors (VDRs), Negative Temperature Coefficient Resistors (NTCs), and Positive Temperature Coefficient Resistors (PTCs), which demonstrate varying resistance based on temperature changes.

PREREQUISITES
  • Understanding of Ohm's law and its mathematical representation (J = σE)
  • Familiarity with non-Ohmic materials, particularly superconductors and semiconductors
  • Knowledge of voltage-current (V-I) characteristics of p-n junction diodes
  • Basic principles of resistors, including NTC and PTC behaviors
NEXT STEPS
  • Research the mathematical modeling of non-linear resistive behavior in superconductors
  • Explore the applications and characteristics of Voltage Dependent Resistors (VDRs)
  • Study the thermal effects on resistance in Negative Temperature Coefficient Resistors (NTCs)
  • Investigate the operational principles of Positive Temperature Coefficient Resistors (PTCs) in circuit design
USEFUL FOR

Students and professionals in electrical engineering, materials science, and physics who are interested in the behavior of non-Ohmic materials and their applications in electronic components.

snatchingthepi
Messages
145
Reaction score
37
So I learned today about the version of Ohm's law where

J = \sigma E

and my professor mentioned that some materials (non-Ohmic materials like superconductors) have "vanishingly small" extra terms that are quadratic or cubic. I'm wondering if anyone can direct me to a source (or even just tell me) where I can find out just how small these terms are for Ohmic (linearly conducting) materials.
 
Engineering news on Phys.org
snatchingthepi said:
So I learned today about the version of Ohm's law where

J = \sigma E

and my professor mentioned that some materials (non-Ohmic materials like superconductors) have "vanishingly small" extra terms that are quadratic or cubic. I'm wondering if anyone can direct me to a source (or even just tell me) where I can find out just how small these terms are for Ohmic (linearly conducting) materials.

The traditional example of non-ohmic materials are semiconductors and semiconductor junctions. The V-I curve of a p-n junction diode is exponential in nature.

But it sounds like you are asking for examples of slight non-linearities in simple conductors? I suppose if the current density is high enough, the transient heating effects might be considered a non-linearity. But the material is still Ohmic, if you use the resistivity for the temperature at each point in the conductor...
 
For example, the Voltage Dependent Resistor that we use for damping voltage spikes.
220px-Typische_Varistorkennlinien.gif

Or the Negative Temperature Coefficient Resistor (NTC)- the resistance decreases when the temperature increases. Since the current through the NTC will generate heat, it can be used to limit "inrush current".
A244Fig01.gif

You also have the Positive Temperature Coefficient Resistor (PTC)- the resistance increases when the temperature increases. Since the current through the PTC will generate heat, it can be used to generate a startup-current that gradually decreases (for example if you want to demagnetize an instrument when you turn it on).
http://www9.dw-world.de/rtc/infotheque/electronic_components/fig1521.gif
 
Last edited by a moderator:
Thank you both.
 

Similar threads

Question about MOSFET Saturation region
  • · Replies 7 ·
Replies
7
Views
3K
Fundamentals of the PN Junction
  • · Replies 12 ·
Replies
12
Views
3K
Undergrad Optimization problem with multiple outputs: impossible?
  • · Replies 6 ·
Replies
6
Views
3K
Understanding the generic nature of linearity in Physics
  • · Replies 2 ·
Replies
2
Views
1K
Relationship between material mass and weight
  • · Replies 5 ·
Replies
5
Views
2K
Courses Math Course Advice -- Harvard freshman planning to double major in physics and mathematics
  • · Replies 41 ·
2
Replies
41
Views
7K
Effects of LLMs on math learning, self taught or otherwise
  • · Replies 10 ·
Replies
10
Views
801
Ohm's Law and its Physical Consequences
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Higgs inflation and quadratic gravity
  • · Replies 1 ·
Replies
1
Views
3K
I have a few questions about refrigeration and AC units
  • · Replies 1 ·
Replies
1
Views
3K