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Resistance
Beginner
Opposition to current.
R = ρL/AR = ρL/A measures opposition to current: longer and thinner wires resist more. Unit: ohm (V/A).
Copper wire of 10 m and 1 mm²: 0.17 Ω.
Resistance depends on material and shape.
In more detail
Resistance is the opposition to current flow in a component, measured in ohms. It depends on the material, length, cross-sectional area and temperature of the conductor.
Real-world uses
- Heating elements use high resistance to produce heat.
- Sensors such as strain gauges use changes in resistance.
- A long, thin heater wire has a high resistance, so it heats a room when a current flows through it.
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Frequently asked questions
What is an ohm?
One volt per ampere.
Why do longer wires have higher resistance?
Because electrons encounter more collisions over a greater length.
Why does a thinner wire have more resistance?
Fewer electrons can pass through a narrow cross-section at once, so the same voltage drives less current.
Related topics in Current Electricity & Circuits
Direction of current · Drift velocity · Ohm's law · Resistivity · Conductivity · Temperature dependence of resistance