Heat engines IB DP Physics Study Notes - 2025 Syllabus
Heat engines IB DP Physics Study Notes
Heat engines IB DP Physics Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Physics syllabus with Students should understand
Cyclic gas processes are used to run heat engines.
A heat engine can operate using different thermodynamic cycles and is characterized by its efficiency, which is given by:
\(\eta = \frac{\text{Useful Work Output}}{\text{Input Energy}}\)The Carnot cycle establishes the theoretical maximum efficiency for a heat engine operating between two heat reservoirs, defined by the equation:
\(\eta_\text{Carnot} = 1 – \frac{T_c}{T_h}\)
where \( T_h \) is the temperature of the hot reservoir and \( T_c \) is the temperature of the cold reservoir, both measured in Kelvin.
Standard level and higher level: There is no Standard level content
Additional higher level: 8 hours
- IB DP Physics 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Physics 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Physics 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
- IB DP Physics 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
Heat Cycles
In a heat cycle, a system goes through several changes as a result of work being done.
- A→B – isovolumetric temperature increase
- B→C – isobaric expansion
- C→D – isovolumetric temperature decrease
- D→A – isobaric compression
Work is done by the gas on the surroundings from B→C and the opposite from D→A. However, mor work is done BY the gas than ON the gas. (How do we know?)
Heat Engines
During a thermal process, there will always be energy loss, so the energy flow can be represented as in the diagram. This leads to the idea of thermal efficiency.
If the internal energy of the hot gas is $Q_h$, and the cold gas is $Q_c$, $W$ represents the useful work done by the engine.
Therefore
$$\eta = \frac{W}{Q_h}$$
Since $W = Q_h – Q_c$,
$$\eta = \frac{Q_h – Q_c}{Q_h} = 1 – \frac{Q_c}{Q_h}$$
Carnot cycles
An idealized version of a thermodynamic cycle is a reversible, 4-stage cycle known as a Carnot cycle. For a Carnot cycle the efficiency of an engine is a theoretical maximum, based on the laws of physics and not based on energy losses in the system.
For a Carnot cycle,
Reversed Processes (Heat Pumps)
When the process is reversed, we have how a refrigerator works.
From C→B, heat is absorbed by the hot object. That heat came from the cold object in A→D. So a cold object is giving heat to a hot object. This can only happen because in D→C, work was done on the gas.
Refrigeration
