AQA A-level Physics Resistors
This page covers the following topics:
Ohmic conductors are conductors that obey Ohm's Law, therefore there is a linear relationship between current and potential difference. Examples of ohmic conductors are electrical wires and resistors.
A filament lamp heats up as current flows through it in a circuit and lights up. As the temperature of the filament lamp increases, its resistance also increases and thus the current is reduced. Filament lamps do not obey Ohm's Law and thus the voltage across them are not directly proportional to the current through them.
A diode is an electrical component used in circuits to allow current to only flow in one direction. This allows for the voltage in a circuit to be controlled and for equipment to be protected. The very high resistance of the diode in one direction means that current can only flow through it in the opposite direction, and thus the diode does not obey Ohm's Law. A small voltage is needed across a diode for it to be able to allow current to flow through it.
Thermistors are elecrtical components used in circuits to detect temperature changes. The resistance of a thermistor changes with temperature. As the temperature increases, the resistance of a thermistor decreases. Low temperatures will cause a big resistance in the thermistor and thus little current will flow through it, whereas at higher temperatures, the reduced resistance will allow for more current to flow through it.
A light dependent resistors (LDR) is an electrical component whose resistance changes depending on the light intensity falling on it. The resistance of an LDR decreases as the light intensity increases. In low lighting, the resistance will be high and the amount of current flowing through it will be low, whereas in brighter places, the resistance will decrease, allownig for more current to flow through it. LDRs can be used in circuits to detect light changes.
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