Electrical resistance and conductance
Fundamental electrical properties quantifying opposition and ease of current flow.
Electrical resistance is a measure of an object's opposition to the flow of electric current, while conductance is its reciprocal, measuring the ease of current passage. These concepts are fundamental to understanding how materials and components behave in electrical circuits, with resistance sharing conceptual parallels with mechanical friction.
- SI unit of resistance
- ohm (Ω)
- SI unit of conductance
- siemens (S)
- Key relationship
- R = V/I, G = I/V = 1/R
- Factors affecting resistance
- material, length, cross-sectional area, temperature, strain
- Ohmic materials
- materials where V and I are directly proportional
Lore & Background
The resistance of an object depends largely on its material; insulators like rubber have high resistance, while conductors like metals have low resistance. However, size and shape also matter—a long, thin wire has higher resistance than a short, thick one. All objects resist current except superconductors, which have zero resistance.
Reader's Guide
Electrical resistance and conductance are defined by the ratio of voltage to current and its reciprocal, respectively. For many materials, voltage and current are directly proportional (Ohm's law), making resistance constant for a given object. This proportionality holds for ohmic materials like wires and resistors. In non-ohmic devices such as diodes or transformers, the ratio varies, leading to concepts like chordal resistance or differential resistance. The resistance of a uniform conductor can be calculated from its length, cross-sectional area, and material resistivity. These principles are essential for designing circuits and understanding how components behave under different conditions.
Did You Know?
- Electrical resistance is measured in ohms (Ω), while conductance is measured in siemens (S).
- Superconductors have a resistance of zero.
- A wire's resistance is higher if it is long and thin, and lower if it is short and thick.
- Ohm's law states that for ohmic materials, voltage and current are directly proportional.
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