Heat Engines and Refrigerators
Physics ⇒ Heat and Thermodynamics
Heat Engines and Refrigerators starts at 11 and continues till grade 12.
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Describe the main difference between a heat engine and a refrigerator.
Explain why a refrigerator cannot cool a room by leaving its door open.
Explain why no heat engine can be 100% efficient.
Explain why the efficiency of real engines is always less than that of a Carnot engine.
A Carnot engine absorbs 1200 J of heat from the hot reservoir and rejects 900 J to the cold reservoir. What is its efficiency?
A Carnot engine operates between 400 K and 200 K. If it absorbs 600 J of heat from the hot reservoir, how much work does it perform?
A Carnot engine operates between a hot reservoir at 500 K and a cold reservoir at 300 K. What is the maximum possible efficiency of this engine?
A Carnot refrigerator operates between 250 K and 300 K. What is its maximum possible coefficient of performance (COP)?
Which of the following best describes a heat engine? (1) A device that converts heat into work (2) A device that converts work into heat (3) A device that transfers heat from a cold reservoir to a hot reservoir (4) A device that stores heat energy
Which of the following devices operates on the reverse principle of a heat engine? (1) Steam turbine (2) Refrigerator (3) Internal combustion engine (4) Electric heater
Which of the following increases the efficiency of a Carnot engine? (1) Increasing the temperature of the hot reservoir (2) Decreasing the temperature of the cold reservoir (3) Both (1) and (2) (4) Neither (1) nor (2)
Which of the following is a correct statement about the direction of heat flow in a refrigerator? (1) From hot to cold (2) From cold to hot (3) No heat flow (4) Both directions simultaneously
Fill in the blank: The maximum efficiency of a heat engine operating between two reservoirs is given by the formula η = 1 - ________.
The coefficient of performance (COP) of a refrigerator is defined as the ratio of ________ to ________.
The efficiency of a heat engine is defined as the ratio of ________ to ________.
Fill in the blank: In a reversible Carnot cycle, the entropy change of the working substance over one complete cycle is __________.
The efficiency of a Carnot engine depends only on the temperatures of the hot and cold reservoirs. True or False?
The second law of thermodynamics implies that it is impossible to construct a device that operates in a cycle and produces no other effect than the transfer of heat from a colder body to a hotter body. True or False?
True or False: A refrigerator transfers heat from a cold reservoir to a hot reservoir by doing work on the system.
True or False: The coefficient of performance of a heat pump is always greater than 1.
