Question

which causes the thermal energy in a building to decrease?
the air conditioner and the heat engine
the furnace and the heat pump
the heat pump and the air conditioner
the heat engine and the furnace

Explanation:

Step1: Understand the function of each device

• Air conditioner: Removes heat from the building (indoor space) and expels it outside, which reduces the thermal energy inside the building.
• Heat engine: Converts thermal energy into mechanical work. It does not directly reduce the thermal energy of a building.
• Furnace: Generates heat and increases the thermal energy of a building.
• Heat pump: Can be used in cooling mode (similar to an air - conditioner in the sense of removing heat from a space). In cooling mode, it takes heat from the building (lower - temperature reservoir) and transfers it to the outside (higher - temperature reservoir), thus decreasing the thermal energy of the building.

Step2: Analyze each option

• Option 1 (the air conditioner and the heat engine): The heat engine does not decrease the thermal energy of the building.
• Option 2 (the furnace and the heat pump): The furnace increases the thermal energy of the building.
• Option 3 (the heat pump and the air conditioner): Both can remove heat from the building (when the heat pump is in cooling mode), decreasing the thermal energy.
• Option 4 (the heat engine and the furnace): The heat engine does not decrease the thermal energy and the furnace increases it.

Answer:

the heat pump and the air conditioner