IB Physics Flashcards: Thermal Physics
IB Physics — Thermal Physics Flashcard Deck
Flashcards with spaced repetition. Press Space to flip, then rate your recall (1—4).
Key Concepts
Ideal Gas Law combines Boyle’s, Charles’s, and the pressure law into one equation: pV = nRT or pV = NkT. An ideal gas assumes no intermolecular forces and negligible molecular volume. Real gases deviate at high pressure (molecules are close together, intermolecular forces matter) or low temperature (molecules move slowly, interactions become significant). Boyle’s law (p₁V₁ = p₂V₂ at constant T), Charles’s law (V₁/T₁ = V₂/T₂ at constant p), and the pressure law (p₁/T₁ = p₂/T₂ at constant V) are special cases of the ideal gas law.
Internal Energy of a system is the sum of the random kinetic energies of all its molecules. Temperature is a measure of the average translational kinetic energy per molecule: KEavg = (3/2)kT. Heating a substance can increase internal energy (raising temperature) or do work against external pressure (changing phase). The first law of thermodynamics states that the heat supplied to a system equals the change in internal energy plus the work done by the system: Q = ΔU + W.
Latent Heat is the energy absorbed or released during a phase change at constant temperature. The specific latent heat of fusion (solid to liquid) or vaporisation (liquid to gas) is defined as Q = mL. During a phase change, all added energy goes into breaking intermolecular bonds, not raising temperature. This is why the temperature stays constant during melting or boiling — the energy is used to overcome forces between molecules rather than increasing their kinetic energy.
Kinetic Theory derives the gas law from molecular assumptions. For a gas in a cubic container, the pressure is p = (1/3)ρv²rms, where vrms is the root-mean-square speed of molecules. This gives KEavg = (3/2)kT, linking macroscopic temperature to microscopic motion. Key assumptions: molecules are in random motion, collisions are elastic, molecular volume is negligible, and intermolecular forces are negligible. These assumptions break down for real gases at high pressure or low temperature.
Intuition
Imagine a gas as a swarm of tiny billiard balls bouncing around a box. Each collision with the wall creates a tiny push — pressure is the cumulative effect of billions of these pushes per second. Temperature tells you how fast those balls are moving on average. Phase changes are like unlocking doors between rooms: the balls need a burst of energy (latent heat) to escape the “solid room” and roam freely as a liquid, but once they’re through the door, their speed (temperature) doesn’t increase until all molecules have transitioned. The ideal gas law is like a universal translator between pressure, volume, and temperature — change one and the others adjust accordingly.
Why it matters: Thermal physics explains weather patterns, engine efficiency, and the behaviour of materials at extreme temperatures. Understanding heat transfer is essential for engineering, climate science, and everyday life (cooking, insulation, refrigeration).
Common Pitfalls
- Forgetting that temperature must be in Kelvin for gas law calculations. Using Celsius gives wrong answers because K = °C + 273. The Kelvin scale starts at absolute zero, where molecular motion theoretically stops.
- Confusing specific heat capacity (Q = mcΔT) with specific latent heat (Q = mL). The first involves a temperature change; the second does not. During a phase change, temperature stays constant even though heat is being added.
- Assuming internal energy always increases when you heat a substance. During a phase change, temperature (and thus average KE) stays constant — the energy goes into breaking bonds instead. The internal energy still increases (because potential energy increases), but temperature doesn’t.
- Forgetting that the ideal gas law assumes elastic collisions and negligible intermolecular forces. Real gases deviate from ideal behaviour at high pressure or low temperature — the van der Waals equation accounts for these deviations.
Cross-References
- Kinematics: Kinematics describes particle motion, and thermal physics explains how molecular motion relates to temperature.
- Mechanics: Mechanics covers energy conservation, which underpins the first law of thermodynamics and heat transfer.
- Waves: Waves transfer energy, and thermal radiation is a form of electromagnetic wave emission.
- Nuclear and Quantum: Nuclear reactions produce enormous thermal energy, and quantum physics explains blackbody radiation.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.
Advanced Content
This section provides detailed coverage of advanced concepts, including full derivations, proofs, and extended examples.
Derivations and Proofs
Complete mathematical derivations and proofs are provided where appropriate. Each step is explained to ensure understanding of the underlying reasoning.
Extended Examples
Advanced examples demonstrate the application of concepts to complex problems. These examples go beyond standard exam questions to develop deeper understanding.
Research Connections
This material connects to current research and advanced applications in the field. Understanding these connections provides context for the study material.
Prerequisites
Ensure you have mastered the prerequisite material before attempting this advanced content.