Chapter 6 Lesson 3 Summary Using Thermal Energy

The total amount of energy in any system, situation, or environment does not ever change.  It may (and often does) change forms, but the total amount of energy does not change.

A device that changes electrical energy into thermal energy is called a heating appliance. 

Curling/straightening irons, clothes irons, clothes dryers, coffee makers, space heaters, and toasters are all examples of heating appliances.

A device that regulates the temperature of a system is called a thermostat.  

• Thermostats contain a bimetallic strip that expands at different rates due to thermal expansion.

• This causes the strip to curl as it heats up (expansion) or cools down (contraction).

• When the bimetallic strip curls, it flips a switch that either starts the furnace, or turns it off.

A device that uses electric energy to transfer thermal energy from a cooler location to a warmer location is called a refrigerator. 

• Thermal energy from the food inside the refrigerator is transferred to a coolant that is colder than the food.  This keeps the food inside the refrigerator cold.

• The coolant then becomes warmer as a result of the thermal energy transfer.

• The coolant then flows out of the refrigerator, where it gives its thermal energy to the surrounding air.  It then expands and cools, flowing back into the refrigerator to begin the cycle of cooling again.

A car engine is a good example of a heat engine. 

A heat engine is a machine that converts thermal energy into mechanical energy.  

Heat engines are usually not very efficient.  Most heat engines only convert about 20% of their chemical potential energy into mechanical energy (from the gasoline they use).