1. Warm Up #4
How does a refrigerator convert thermal energy?

2. Lesson 3: Using Thermal Energy
Ch. 13 Thermal Energy
Lesson 3: Using Thermal Energy

3. Essential Questions How does a thermostat work?
How does a refrigerator keep food cold?
What are the energy transformations in a car engine?

4. Thermal Energy Transformations
Other forms of energy can be converted into thermal energy
Ex. Stretching a rubber band repeatedly makes it hot
Thermal energy can be converted into other forms of energy
Ex. Thermostats transfer thermal energy into mechanical energy

5. Heating Appliances
Heating appliances – a device that converts electric energy into thermal energy
Ex. Curling irons, coffeemakers, clothes irons
Thermal energy that’s generated from most electronics isn’t used for any purpose
What does it turn into?

6. Thermostats
Thermostat – a device that regulates the temperature of a system
Bimetallic coil is made of 2 types of metals
They join together and bend into a coil
Inside coil expands and contracts more than
outside one
When it warms, thermal energy causes the coil to
uncurl slightly, which moves a switch to turn off the
furnace
When it cools, the metal contracts, curling tighter,
which turns on the furnace

7. Refrigerators
Refrigerator – a device that uses electric energy to transfer thermal energy from a cooler location to a warmer location
Pipes that surround the refrigerator are filled with a coolant that flows through
Thermal energy from inside the refrigerator transfers to the coolant, keeping the inside cold
The coolant starts as a liquid, cools, becomes a gas that flows through the pipes absorbing thermal energy

8. Refrigerators
The coolant gas becomes warmer as the inside of the refrigerator becomes cooler
The coolant becomes compressed at the bottom of the fridge in an electric compressor, which increases thermal energy
Thermal energy from here flows behind the fridge as the coils are warmer than behind the fridge
As thermal energy is removed from the gas, it condenses and becomes a liquid, then it’s pumped back up and repeats

9. Can Thermal Energy Be Used To Do Work? ACTIVITY
Add 10mL of water to a 100mL beaker
Place a square of aluminum foil over the top of the beaker
Place beaker on a hot plate and turn it on.
What do you observe happening?
Is thermal energy used to do work? Explain.
Is thermal energy transformed into another form of energy? If so, what other form of energy?

10. Heat engines Heat engine – a machine that converts
thermal energy into mechanical energy
This is what moves a vehicle
A cylinder with a piston moves up and down
1 end of the cylinder a spark ignites a fuel-air mixture, which expands and pushes the piston down
This is due to the chemical energy converting to thermal energy, which some immediately converts to mechanical energy
Only about 20% is actually converted, the rest is lost to the environment

11. Review
Suppose you pointed a hair dryer at the device pictured and turned on the hair dryer. What would happen?
Describe the path of thermal energy in a refrigerator.