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Physics Chapter 8 : Topic 17
Refrigerators as Reverse Heat Engines
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A refrigerator works on the principle of:
Reasoning: A refrigerator uses work input to transfer heat from a cold region to a hot region, which is the reverse operation of a heat engine.
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The main difference between a heat engine and a refrigerator is:
Reasoning: A heat engine produces work from heat flow, while a refrigerator consumes work to transfer heat against natural flow.
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A refrigerator transfers heat:
Reasoning: Work is supplied to remove heat from a low-temperature region and release it to a higher-temperature region.
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The working principle of a refrigerator is based on:
Reasoning: The second law explains that heat cannot naturally flow from cold to hot without external work.
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In a refrigerator, the cold reservoir is:
Reasoning: The refrigerator removes heat from the inside compartment (cold reservoir).
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In a refrigerator, the hot reservoir is:
Reasoning: Heat removed from inside is released to the surroundings through the condenser.
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The energy input required by a refrigerator is:
Reasoning: A refrigerator requires electrical energy to run the compressor and transfer heat.
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A heat engine differs from a refrigerator because:
Reasoning: The direction of energy conversion is opposite in the two devices.
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The main function of the compressor in a refrigerator is to:
Reasoning: The compressor increases pressure and temperature of the refrigerant using external work.
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The refrigerant in a refrigerator acts as:
Reasoning: The refrigerant absorbs and releases heat during the refrigeration cycle.
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If a refrigerator removes $\mathbf{500\ J}$ heat from the cold space and receives $\mathbf{100\ J}$ work, heat released to surroundings is:
Reasoning: $\mathbf{Q}_{\mathbf{H}}\mathbf{=}\mathbf{Q}_{\mathbf{C}}\mathbf{+ W = 500 + 100 = 600\ J}$
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A refrigerator does not violate the second law because:
Reasoning: External work allows heat transfer in the opposite direction.
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In a refrigerator, the relationship between heat transfers and work is:
Reasoning: Heat released to surroundings equals heat removed from inside plus work supplied.
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If the power supply to a refrigerator is removed:
Reasoning: The refrigeration cycle requires continuous work input.
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The purpose of insulation in a refrigerator is to:
Reasoning: Insulation reduces heat gain from the environment.
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A heat engine and refrigerator both involve:
Reasoning: Both devices involve heat transfer, but their purposes are opposite.
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A heat engine:
Reasoning: Heat engines convert part of heat energy into mechanical work.
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A refrigerator is sometimes called a reversed heat engine because:
Reasoning: The energy flow direction is reversed compared with a heat engine.
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In a refrigerator, work input causes:
Reasoning: Work allows heat movement against the natural direction.
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Which device is an example of a refrigerator?
Reasoning: Air conditioners remove heat from indoor spaces using the refrigeration principle.
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The performance of a refrigerator is measured by:
Reasoning: Refrigerators are evaluated by $\mathbf{COP}$ rather than efficiency.
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The coefficient of performance of a refrigerator is:
Reasoning: $\mathbf{COP}$ is the ratio of heat removed from the cold space to the work input.
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A refrigerator with a higher $\mathbf{COP}$ is:
Reasoning: Higher $\mathbf{COP}$ means more heat is removed per unit work supplied.
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If a refrigerator removes $\mathbf{900\ J}$ heat using $\mathbf{300\ J}$ work, its $\mathbf{COP}$ is:
Reasoning: $\mathbf{COP =}$ $\frac{\mathbf{Q}_{\mathbf{C}}}{\mathbf{W}}\mathbf{=}\frac{\mathbf{900}}{\mathbf{300}}\mathbf{= 3}$
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The back side of a refrigerator feels warm because:
Reasoning: The condenser releases heat to the surroundings.
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Opening a refrigerator door does not cool the room because:
Reasoning: The heat removed from inside plus electrical energy is released into the room.
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A refrigerator cannot cool a room with its door open because:
Reasoning: The refrigerator transfers more heat into the room than it removes.
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The ideal refrigerator is similar to a Carnot engine because:
Reasoning: An ideal refrigerator is based on the reversed Carnot cycle.
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A refrigerator moves heat from cold to hot regions, which:
Reasoning: The second law requires work input for this process.
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The working principle of a refrigerator can be summarized as:
Reasoning: A refrigerator reverses the operation of a heat engine by using work to move heat against its natural direction.
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