Which is a correct statement about an ideal heat engine? Tick (✔) one box - AQA - A-Level Physics - Question 5 - 2021 - Paper 6
Question 5
Which is a correct statement about an ideal heat engine? Tick (✔) one box.
The efficiency is increased when the kelvin temperatures of the hot source and the cold s... show full transcript
Worked Solution & Example Answer:Which is a correct statement about an ideal heat engine? Tick (✔) one box - AQA - A-Level Physics - Question 5 - 2021 - Paper 6
Step 1
Which is a correct statement about an ideal heat engine?
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Answer
The efficiency is 50% when the kelvin temperature of the hot source is twice the kelvin temperature of the cold sink.
Step 2
Determine the coefficient of performance COP_ref of the refrigerator.
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Answer
To find the coefficient of performance for the refrigerator, we use the relation:
COPref=WQh
Where:
Qh is the heat extracted from the cold space,
W is the work input to the engine.
Given the efficiency (η) of the engine is 0.33:
W=Qh−Qc,
Where Qc is the heat rejected to the cold space. Using the efficiency relation:
η=QhW=0.33,
We can rearrange this to find W:
W=0.33Qh.
So, substituting W into the COP formula:
COPref=0.33QhQh=0.331≈3.03.
