Thermistor A transducer which converts temperature (heat) to resistance (an electrical property).
This type of variable capacitor is designed to be set when a circuit is made and then left without further adjustment.
Loudspeaker A transducer which converts electrical energy to sound.
Transistor NPN A transistor amplifies current and can be used with other components to make an amplifier or switching circuit. This symbol is for a bipolar junction transistor (BJT), the type you are most likely to use at first.