LIGHT DEPENDENT RESISTOR
This is a type of resistor which has a resistance that changes with the amount of LIGHT that falls on it. The light energy produces more free electrons which increases the current for a certain voltage across the LDR which means a drop in resistance.
In the DARK its resistance is LARGE (millions of ohms), in the LIGHT its resistance is SMALL (tens of ohms). Very little current will flow through it in the dark.
LDRs are used as light sensors.
THERMISTOR
This is a type of resistor which has a resistance that changes with TEMPERATURE. The increasing temperature produces more free electrons and so the resistance falls.
At LOW TEMPERATURE its resistance is LARGE (thousands of ohms), at HIGH TEMPERATURE its resistance is SMALL (tens of ohms). Very little current will flow through it when it is cold. This means that its resistance increases as the temperature falls.
Thermistors are used as temperature sensors