Thermal Physics

What Thermal Physics covers

Thermal Physics is examined in Component 1, Newtonian Physics. It covers internal energy, absolute zero and temperature, internal energy of an ideal monatomic gas, heat as energy in transit, thermal equilibrium, work done by a gas, the first law of thermodynamics and specific heat capacity.

The 8 subtopics

Each one has its own page.

• Internal energyRecall questions on the definition of internal energy as the sum of the random kinetic and potential energies of the particles, why it is a property of the state rather than of a process, what changes it, and how it differs for an ideal gas from a real one.Open →
• Absolute zero and temperatureRecall questions on the kelvin scale and converting to and from Celsius, the meaning of absolute zero, why no temperature can fall below it, extrapolating a gas law graph to estimate it, and why absolute temperature is used in every gas equation.Open →
• Internal energy of an ideal monatomic gasRecall questions on U = (3/2)nRT and its derivation from the mean molecular kinetic energy, why an ideal gas has no molecular potential energy, worked calculations for a stated amount of gas, and how the internal energy changes with temperature.Open →
• Heat as energy in transitHeat in the thermodynamic sense, condition under which heat enters a system and condition under which heat leaves a system.Open →
• Thermal equilibriumRecall questions on what thermal equilibrium means, the direction of energy flow between bodies at different temperatures, what happens when equilibrium is reached, and why temperature rather than internal energy decides the direction of flow.Open →
• Work done by a gasWhy work is described as energy in transit and sign of W when a gas is compressed.Open →
• The first law of thermodynamicsRecall questions on ΔU = Q − W with the sign convention for each term, applying it to a gas being compressed and expanding, the work done as pΔV, adiabatic and isothermal changes, and worked problems in which two of the three quantities are given.Open →
• Specific heat capacitySpecific heat capacity, equation Q = mcΔθ, defining every symbol and its unit and why water is a good coolant in a car engine.Open →

What you need to know

Answer each one before you reveal it.

Take Thermal Physics further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Positive Q vs Positive W

  Positive Q: energy has entered the system as heat. Positive W: energy has left it as work done on the surroundings.

Questions from this topic

Each one with the model answer underneath.

1. 1

   Define the internal energy of a system.

   Model answer

   The internal energy of a system is the sum of the random kinetic energies and the potential energies of all its molecules.

2. 2

   Which part of the internal energy of a substance depends on the separation of its molecules?

   Model answer

   The potential energy contribution depends on the separation, because it arises from the forces the molecules exert on one another.

3. 3

   Which part of the internal energy of a substance depends on the temperature?

   Model answer

   The random kinetic energy contribution depends on the temperature, since the mean molecular kinetic energy rises with the thermodynamic temperature.

4. 4

   Why is the kinetic energy of a moving car not part of the internal energy of the car?

   Model answer

   Internal energy counts only the random motion of the molecules relative to the body, whereas the car's kinetic energy comes from the ordered motion of the whole body.

5. 5

   Explain why melting a solid at its melting point increases the internal energy without changing the temperature.

   Model answer

   The energy supplied goes into separating the molecules against their mutual attraction, so the molecular potential energy rises while the mean kinetic energy, and therefore the temperature, stays the same.

6. 6

   Explain why the internal energy of a real gas rises when it expands at constant temperature.

   Model answer

   The molecules move further apart against their weak mutual attractions, so their potential energy increases while their mean kinetic energy is unchanged.

What is inside Levo

Six ways to work the same material.

Thermal Physics revision questions

What does Thermal Physics cover in Eduqas A-Level Physics?

8 subtopics: internal energy, absolute zero and temperature, internal energy of an ideal monatomic gas, heat as energy in transit, thermal equilibrium, work done by a gas, the first law of thermodynamics and specific heat capacity. Each one has its own page with questions and model answers.

How is Thermal Physics organised?

By the Eduqas A420QS specification, subtopic by subtopic, so it matches the order you are taught it in.