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

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

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

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

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?

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

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

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

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?

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

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.