Thermodynamics

The coefficient of performance (COP) of a refrigerator is the ratio of heat removed to work input, which can be greater than, equal to, or less than one depending on the operating temperatures. Distractor B is incorrect because a COP can easily exceed 1, especially when the temperature difference between the reservoirs is small.

Under the standard physics convention where W represents the work done by the system on its surroundings, the change in internal energy equals heat added minus work done. Option A is incorrect under this convention because work done by the system decreases its internal energy.

Under the standard physics convention where W represents the work done by the system on its surroundings, the change in internal energy equals heat added minus work done. A diagram for this topic isn't available yet — the worked example below walks the same reasoning step by step.

• !Option A is incorrect under this convention because work done by the system decreases its internal energy.
• !Option D is incorrect because J/K represents heat capacity, which does not normalize for the mass of the substance.
• !Distractor B is incorrect because a COP can easily exceed 1, especially when the temperature difference between the reservoirs is small.
• !Option A is incorrect because a process where volume stays constant is termed isochoric, while option C describes an isothermal process.

Answer each from memory — you'll see instantly whether you're right and why.

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