Final answer:
The bimetallic strip is the most common temperature sensing element in mechanical thermostats, whereas thermistors are often used in electronic thermostats due to their temperature-dependent resistance.
Step-by-step explanation:
The most common temperature sensing element used for mechanical thermostats is the bimetallic strip. Bimetallic strips are made by bonding two different metals with different thermal expansion coefficients together. As the temperature changes, the difference in expansion rate between the two metals causes the strip to bend. This bending can then be used to mechanically control a switch within a thermostat, enabling the device to turn heating or cooling systems on or off in response to temperature changes. Another common element in electronic thermostats is the thermistor. Thermistors are semiconductor devices whose resistance changes with temperature. This change in resistance can be accurately measured and converted into a temperature reading.