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Thermodynamics: Exploring Heat, Work, and Energy in A-Level Science
What Is Thermodynamics?
Thermodynamics is the study of heat, work, and energy, and how they interact in physical systems.
Laws of Thermodynamics
First Law of Thermodynamics
Energy is conserved:
![\[ \Delta U = Q - W \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-0652b09261326fa359a3e13a806da76d_l3.png "Rendered by QuickLaTeX.com")
Where:
: Change in internal energy (J)
: Heat added to the system (J)
: Work done by the system (J)
: Change in internal energy (J)
: Heat added to the system (J)
: Work done by the system (J)Second Law of Thermodynamics
Heat flows from hot to cold, and entropy always increases in an isolated system.
Third Law of Thermodynamics
At absolute zero (
), the entropy of a perfect crystal is zero.
Heat Engines
Carnot Engine
The most efficient theoretical heat engine.
Efficiency:
![\[ \eta = 1 - \frac{T_c}{T_h} \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-cb85c11f209457feec15343ed618894f_l3.png "Rendered by QuickLaTeX.com")
Where:
: Cold reservoir temperature (K)
: Hot reservoir temperature (K)
: Cold reservoir temperature (K)
: Hot reservoir temperature (K)Real-Life Heat Engines
Examples include car engines and power plants, where thermal energy is converted to mechanical work.
Applications of Thermodynamics
Refrigeration
Thermodynamics principles are used to extract heat from a cold area and release it in a warm area.
Renewable Energy
Used in the design of solar thermal power plants.
Medicine
Cryotherapy relies on thermodynamic principles for therapeutic benefits.
Example Problem
A heat engine operates between 
and 
. Find its efficiency.
- Formula:
![\[ \eta = 1 - \frac{T_c}{T_h} \]](data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSI4NSIgaGVpZ2h0PSIzOSIgdmlld0JveD0iMCAwIDg1IDM5Ij48cmVjdCB3aWR0aD0iMTAwJSIgaGVpZ2h0PSIxMDAlIiBzdHlsZT0iZmlsbDojY2ZkNGRiO2ZpbGwtb3BhY2l0eTogMC4xOyIvPjwvc3ZnPg== "Rendered by QuickLaTeX.com")
- Substitute Values:
![\[ \eta = 1 - \frac{300}{600} = 0.5 \, \text{or} \, 50\% \]](data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxOTQiIGhlaWdodD0iMzYiIHZpZXdCb3g9IjAgMCAxOTQgMzYiPjxyZWN0IHdpZHRoPSIxMDAlIiBoZWlnaHQ9IjEwMCUiIHN0eWxlPSJmaWxsOiNjZmQ0ZGI7ZmlsbC1vcGFjaXR5OiAwLjE7Ii8+PC9zdmc+ "Rendered by QuickLaTeX.com")
![\[ \eta = 1 - \frac{300}{600} = 0.5 \, \text{or} \, 50\% \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-75b93628972d37180288ab17c7c123a9_l3.png "Rendered by QuickLaTeX.com")
Common Mistakes in Thermodynamic Calculations
- Forgetting to use Kelvin for temperature
- Mixing up heat added () and work done ()
- Ignoring inefficiencies in real-world systems
Practice Questions
- A heat engine absorbs
of heat and performs 
of work. Calculate the change in internal energy. - Explain the significance of the second law of thermodynamics.
- Describe one application of thermodynamics in renewable energy.
of heat and performs 
of work. Calculate the change in internal energy.