Preset variable resistor A preset is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than standard variable resistors so they are sometimes used in projects to reduce the cost.
Piezo Transducer A transducer which converts electrical energy to sound
A variable capacitor is used in a radio tuner.
Thermistor A transducer which converts temperature (heat) to resistance (an electrical property).