Physics · Class 11

Set the temperature limits of an engine

A heat engine must reject some heat to the cold reservoir. The reversible Carnot efficiency depends only on absolute reservoir temperatures. Increasing their temperature separation increases the ideal efficiency.

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Set the temperature limits of an engine

கார்னோ இயந்திரத்தின் திறன் 1 − Tc/Th. வெப்பநிலைகள் கெல்வினில் இருக்க வேண்டும்; குளிர் தேக்கத்திற்கு வெப்பம் வெளியேற்ற வேண்டும்.

Key notes, relationships and model limits

Key relationship

ηCarnot=1−Tc/Th; W=ηQh; Qc=QhTc/Th; COPfridge=Tc/(Th−Tc).

Remember

Common trap

Using Celsius in the temperature ratio gives an incorrect efficiency.

Model limits

Reversible efficiency is an upper bound between two fixed-temperature reservoirs in kelvin; real engines have lower efficiency. This lab compares efficiency and refrigerator COP but does not trace the four Carnot-cycle stages.

What you will learn

Apply the reversible efficiency bound and an engine energy balance.

Try the experiment

Try both scenarios, change one control, and predict the result before checking the graph and readouts.

Think of it this way

Change one input while keeping the others fixed, as you would in a controlled experiment.

Worked example

From Qh=1000 J, this engine produces W=500 J and rejects Qc=500 J. The reversed refrigerator has COP=300/(600−300)=1.

Why this matters

The model connects set the temperature limits of an engine with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

What is Carnot efficiency between 600 K and 300 K?

100%
0.5, or 50%
25%

Read the explanation

η=1−300/600=0.5.

Course connection: Class XI Chapter 11. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.