Devices and resistance

An LDR is a resistor that changes its resistance depending on how much light there is.

In bright light -  the resistance falls.

In darkness - the resistance is highest.

A thermistor is a resistor that changes its resistance depending on temperature.

In hot conditions - the resistance drops.

In cool conditions - the resistance goes up.

Resistors get hot when an electric current passes through them-

When there is an electric current in a resistor, there is an energy transfer which heats the resistor.

This energy transfer is due to electrons colliding with ions in the lattice that make up the resistor as they move through it.

These collisions give the ions in the lattice extra energy, which is emitted as heat. This heating effect increases the resistors resistance - so less…