Circuits - AQA SynergyDifferent resistors

Carbon resistors have a constant resistance regardless of the conditions in which they are used. However, the resistance of other different materials can be affected in different ways.

Variable resistor

A variable resistor has its resistance changed by altering the length of material within the resistor. The further the electrons have to travel through the material, the more opportunities there are for collisions between the electrons and the atoms/ions within the material.

Filament lamp

A filament lamp gets hot when a current passes through it. However, as the temperature rises the resistance of the wire increases. This means any extra current passing will require a greater increase in potential difference than before.

Thermistor

The resistance of a thermistor depends on its temperature. At low temperatures, the thermistor has a high resistance. As the temperature increases, the resistance decreases. The increased vibrations of the particles within the material knock electrons out of orbitals and, therefore, produce more electrons that are free to move around the material, making it easier for current to flow, reducing resistance.

Light-dependent resistor (LDR)

The resistance of a LDR depends on light intensity. At low light levels, the LDR has a high resistance. As the light intensity increases, the resistance decreases. LDRs are made of materials (semiconductors) which have electrons knocked out of orbitals when photons of light hit them. In the light, there are more electrons that are free to move around the material, making it easier for current to flow, reducing resistance.

Semiconductor diode

A semiconductordiode allows current to flow in one direction only. Current will not flow in the other direction. Diodes are used to convert an alternating current into a direct current.