electrical resistance
Let an agent explain electrical resistance, its units, laws and measurement, distinguish resistance from resistivity, impedance and conductance, and support calculation and teaching.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
written by Claude from model knowledge without web access - no source was read, every claim is a lead to verify
Researched by: Claude
Purpose and description
Let an agent explain electrical resistance, its units, laws and measurement, distinguish resistance from resistivity, impedance and conductance, and support calculation and teaching.
The opposition a material or component offers to the flow of electric current, defined as voltage divided by current and measured in ohms; resistance depends on material, dimensions and temperature, and the related quantity impedance extends the idea to alternating current by including reactance, while resistivity describes the material independent of shape.
What it is for: Not for anything; a property that governs current flow and is exploited in resistors and heaters.
It can be explain resistance and Ohm law; distinguish resistance, resistivity, impedance and conductance; calculate resistance for circuits and conductors; relay measurement methods.
Distinguishing features
Ratio of voltage to current
Ohmic and non-ohmic behaviour
Temperature dependence
Scalar, unlike complex impedance
What it looks like
Not visible; measured with an ohmmeter and marked on resistors by colour bands or codes.
Physical character
unit: ohm V per A - SI derived unit
copper resistivity: about 1.7 times 10 to the minus 8 ohm metre - at 20 degrees C
temperature coefficient of copper: about 0.004 per degree C
How it is recognised
Voltage over current, in ohms
Depends on material, geometry and temperature
Impedance includes reactance; resistivity is per material
Related models
is a kind of - a scalar quantity
is measured in - the SI unit
is defined by - voltage over current
is generalised by - for alternating current
In practice
Families and kinds
resistance of conductors and components
resistivity of materials
sheet resistance of thin films
contact resistance
impedance and characteristic impedance in AC circuits
biological resistances such as transepithelial resistance
Identifiers
SI unit symbol ohm omega symbol
quantity symbol R ISO 80000-6
Standards and regulation
SI Brochure from BIPM
ISO 80000-6 electromagnetic quantities
IEC standards for resistors and measurement
Failure modes and hazards
Overheating from high resistance in connections
Confusing resistance with impedance or resistivity
Measurement errors from lead and contact resistance
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 4 bundles · 8 layers · 8 findings · 16 questions.
Concept What resistance is.
Definition.
Definition
Definition and law.
Definition
Definition.
- What is electrical resistance, and what does Ohm law state and not state? definition
- Is the question about resistance, resistivity, impedance or conductance? boundary
Factors
What determines it.
Factors
Factors.
- How do material, length, cross-section and temperature determine resistance? definition
- Which entry fits resistivity? action
Calculate Circuits and calculation.
Computation.
Circuits
Series and parallel.
Circuits
Circuits.
- How are resistances combined in series and parallel, and how is a circuit solved? action
- What is the result for the circuit in question? measurement
Power
Power and heating.
Power
Power.
- How does resistance relate to power dissipation and heating? definition
- Which entry fits Joule heating? action
Measure Measurement.
Measurement.
Methods
Methods.
Methods
Methods.
- How is resistance measured, from ohmmeters to four-terminal sensing? measurement
- What accuracy and sources of error apply? measurement
Components
Resistors.
Components
Components.
- How are resistors specified and marked? provenance
- Which entry fits resistors? action
Learn Physics and teaching.
Study.
Physics
Microscopic origin.
Physics
Physics.
- What is the microscopic origin of resistance, and what are superconductivity and non-ohmic behaviour? provenance
- Which entry fits superconductivity? action
Teach
Teaching.
Teach
Teaching.
- How is resistance taught, and which misconceptions arise? provenance
- Which references are standard? provenance
What the second pass must settle
- Should impedance be a separate entry?
- How should material data be linked?
- The registry entry has merged aliases for impedance and biological resistances; should they be split off?