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Resistance
The ratio of voltage across to the current in a component.
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1. Resistance and Ohm's Law
V is always equal to IR, but V is not always proportional to I. If that doesn't make sense then you need to see this video and the next one on IV characteristics.
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2. Resistance and Temperature
Why does the resistance of a conductor increase with temperature? This model of the vibrating ions is one way to visualise what is happening inside the lattice.
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3. Conductance
Just like resistance is an indication of how much current is impeded, conductance tells us how well something conducts electricity.
(This is not needed for all exam boards - check with your specification)
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4. Liquid Nitrogen and High Voltages
As you cool a substance its resistance decreases (if you go extremely low you get into the realms of superconductivity where R = 0).
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