A resistor is an electrical componant that restricts the flow of electric current.
the current flowing through a resistor at a constant temperature is directly proportional to the potential difference across it-----Ohms Law
Heats up when electric current passes through
lamp resistance increases as the temperature increases. Current flowing is not directly proportional to the voltage accross it.
A diode has a very high resistance in one direstion, meaning current only ever flows in the other direction. Good for warning lights etc
Light emitting Diodes (LEDS) produce light when a current flows through them in a forward direction
Often used as indicator lights. Use much smaller current, increased use
Thermistors and LDRs
Thermistors are used as temperature sensors, eg fire alarms. The resistance decreases as the temperature increases
LDRs are used to detect light levels, eg auto security lights. The resistance decreaes as the light intensity increases.