Electrical resistance is the property to oppose electric current flow, measured in ohm (Ω), showing how much a conductor (e.g. wire) resists electrons flow if it has voltage.
Its reciprocal quantity is electrical conductance, measuring the ease electric current passes. Resistance shares some conceptual parallels to mechanical friction.
Electrical conductance is measured in siemens (S) (formerly called 'mho' '℧').
An object's resistance depends mainly of what it's made of. Objects of electrical insulators (e.g. rubber) often have high resistance and low conductance. Electrical conductors objects (e.g. metals) have low resistance and high conductance.
This fact is quantified by resistivity/conductivity. A material's nature isn't the only factor in resistance and conductance; it also depends on its size, shape as the properties are extensive instead intensive.
Narrow pipe = high resistance (less flow)
Wide pipe = low resistance (more flow)
Long pipe = more resistance than short ones
All objects resist electrical current, except superconductors, which have 0 resistance.
What causes resistance
Electron collisions: As electrons move into conductors, they collide via atoms, losing energy (like friction).
Material properties: Some materials (e.g., copper) have low resistance, some (e.g., rubber) high resistance.
Resistance often increases by temperature (except in semiconductors like silicon).
Factors affecting resistance
Length (L): longer wires = higher resistance
Cross-sectional area (A): thicker wire = lower resistance
Resistivity (ρ): material's intrinsic property
Fixed/Constant resistance is for circuits to control current.
Variable resistance is adjustable (e.g., volume knobs).
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