GCSE Physics · AQA 8463 · Topic 4.2.1
Current, potential difference and resistance
Key points
- Learn the circuit symbols: cell, battery, switch, lamp, fuse, resistor, variable resistor, diode, LED, LDR, thermistor, ammeter and voltmeter.
- Current is the rate of flow of charge, (charge in coulombs, time in seconds). An ammeter goes in series.
- Potential difference is measured with a voltmeter placed in parallel. Resistance: .
- An ohmic conductor at constant temperature has a straight-line – graph through the origin. A filament lamp's resistance rises as it gets hotter.
- A diode lets current flow in one direction only (very high resistance in reverse).
- A thermistor's resistance falls as temperature rises; an LDR's resistance falls as light intensity rises. They are used in thermostats and automatic night lights.
- Required practicals: investigate the resistance of a wire (length) and the – characteristics of components.
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Every circuit question rests on three quantities: current, potential difference and resistance. This sub-topic defines them, links them with two key equations and shows how different components respond when the potential difference across…
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