RESISTANCE | RESISTIVITY | CONDUCTANCE | CONDUCTIVITY | EFFECT OF TEMPERATURE ON RESISTANCE
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A friendly guide to resistance and related concepts
Resistance, resistivity, conductance and conductivity are fundamental ideas you'll meet in circuits and materials science. Think of them as different ways to describe how easily electrons move. Below we explain each idea with short tricks, familiar examples, and small mental models you can use on exams or while designing simple circuits.
What it is: Resistance is the opposition a material or component offers to the flow of electric current. Measured in ohms (Ω), a higher resistance means less current for a given voltage.
Quick trick: Imagine water flowing through a pipe — resistance is like a narrow section that slows the water down. Wider pipe = lower resistance.
What it is: Resistivity is a material property that tells how strongly a material opposes current per unit length and cross-section. It depends on the material, not the shape.
Formula: R = ρ · (L / A) where L is length, A is cross-sectional area. Smaller area or longer wire → higher resistance.
Exam tip: If two wires are of the same material, compare length and area. If different materials, check resistivity values first.
What it is: Conductance is simply the reciprocal of resistance: G = 1 / R. Measured in siemens (S).
Think: If resistance is friction, conductance is slipperiness — bigger G means easier current flow.
What it is: Conductivity is the reciprocal of resistivity: σ = 1 / ρ. It measures how well a material conducts electricity.
Metals like copper have high conductivity; insulators like glass have very low conductivity.
Overview: Temperature changes how easily electrons move. For most metals, resistance increases with temperature; for semiconductors, resistance usually decreases as temperature rises.
Linear approximation for metals: R(T) = R0 [1 + α (T - T0)], where α is the temperature coefficient. Remember: positive α → resistance increases with temperature.
Practical example: A filament bulb gets hot, its resistance rises — that limits current and shapes the bulb's behaviour.
Short tricks & familiar examples
- Series resistors: add them. Parallel: reciprocals add. Use quick checkboxes in exams.
- Wires: longer = more resistance; thicker = less resistance.
- Temperature: metals → +R, semiconductors → -R (usually).
These principles will make calculations faster and help you pick the right materials when prototyping: choose lower resistivity metals for power wires, and consider temperature coefficients for precision sensors.
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Selected helpful posts from Electrical Zindagi — visit the site for more topic-specific notes and tutorials.
| Title | Link |
|---|---|
| Basic Electronics: Resistors & Types | Visit |
| Ohm's Law & Circuit Tricks | Visit |
| Temperature Effects on Semiconductors | Visit |
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