2.2Thermal Physics
Thermal Properties and Temperature — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
15 min read 25 parts Lesson 12 of 45 Unit quiz
Lesson summary
2.2 Thermal Properties and Temperature (Part 1) — IGCSE PHYSICS notes: Explain thermal expansion with particles, define internal energy, and calculate energy changes with specific heat capacity.What happens — when a material is heated at constant pressure its temperature rises, i…
- Particle explanation
- Liquid-in-glass thermometer
- Bimetallic strip
- Definition
- Water has a high c
- Rearranging
Part 1 of 7Thermal expansion
Thermal expansion
What happens
- What happens when a material is heated at constant pressure its temperature rises, its volume increases and its density falls.
Particle explanation
- Particle explanation thermal energy is transferred, so the particles gain kinetic energy.
- The temperature rises.
- The particles vibrate or move faster.
- They move further apart.
- The separation increases and the material gets bigger.
Key point
- Key point the material expands, not the molecules, because only the separation changes.
Part 2 of 7Expansion in solids, liquids and gases
| State | Expansion | Explanation |
|---|---|---|
| Solid | Slight | Strong forces hold particles in fixed positions so they only vibrate a little further apart |
| Liquid | More than solids | Weaker forces let particles move further apart |
| Gas | Greatest | Almost no forces between particles so they spread much further |
Part 3 of 7Uses and consequences of expansion
1Liquid-in-glass thermometer
- Liquid-in-glass thermometer a liquid in a bulb expands along a thin capillary tube against a scale.
- A narrower tube makes it more sensitive because the same expansion moves further.
- Thinner glass around the bulb makes it respond faster.
2Bimetallic strip
- Bimetallic strip two metals joined together expand by different amounts, so the strip bends at a set temperature and can close a circuit.
3Buckling
- Buckling hot railway tracks, roads and bridges may buckle.
- Gaps are built in to allow room for expansion.
Part 4 of 7Internal energy and temperature
Internal energy
- Internal energy the total energy stored inside a system by its particles because of their motion and positions.
- Motion gives kinetic energy and relative positions give potential energy.
Temperature
- Temperature it is related to the average kinetic energy of the particles.
- A higher temperature means a higher average kinetic energy and a higher internal energy.
Part 5 of 7Specific heat capacity
Definition
- Definition the specific heat capacity c is the energy needed per unit mass per unit temperature rise.
- It is the energy to raise 1 kg of a substance by 1 °C.
Equation
- ΔE = mcΔθ,
- or c = ΔE ÷ (mΔθ).What the symbols mean: E, Q or q = energy transferred (J) · m = mass · c = specific heat capacity (J kg−1 °C−1; water 4.18 J g−1 °C−1) · ΔT or Δθ = temperature change (°C or K)
- (kg; g in chemistry calorimetry)
- or c = ΔE ÷ (mΔθ).
- ΔE in joules, m in kilograms, c in J/kg °C and Δθ in °C.
Meaning
- Meaning a low value heats and cools quickly, and a high value heats and cools slowly.
- A metal pan warms faster than the water in it because metal has the lower c.
Part 6 of 7More key facts: Thermal Expansion, Internal Energy and Specific Heat Capacity
1Water has a high c
- Water has a high c it takes a lot of energy to warm water, which is why it is used in central heating and cooling systems.
2Rearranging
- Δθ = ΔE ÷ (mc) and m = ΔE ÷ (cΔθ).
3Expansion order
- Expansion order gases expand most, then liquids, then solids.
4Bimetallic strip direction
- Bimetallic strip direction it bends towards the metal that expands less.
Part 7 of 7More from the specification
More from the specification
Distinction Between Boiling and Evaporation
- Evaporation occurs exclusively at the liquid surface at any temperature as energetic particles escape,
- whereas boiling occurs throughout the liquid at a fixed boiling point.
Melting Point and Latent Heat
- During melting, thermal energy is absorbed to weaken intermolecular bonds without raising temperature, keeping substance temperature steady at the melting point.
Specific Heat Capacity Experiment
- Using an electric immersion heater connected to a voltmeter and ammeter, an investigator can measure current and voltage over time to determine thermal energy input.
Calculating Absorbed Thermal Energy
- By recording the temperature change of a known liquid mass heated by an immersion heater, specific heat capacity is calculated using Q = m * c * Delta T.
Evaporation
- Escape of the most energetic molecules from a liquid surface at any temperature
Boiling
- Liquid becoming gas throughout the liquid at the boiling point
Melting
- Change from solid to liquid.
Current
- Flow of electrons in a circuit.
Heater
- A device that transfers electrical energy to the thermal store.
Immersion heater
- Electric heater placed in a liquid or block to supply energy
Intermolecular force
- An attractive force between particles.
Key terms
| Term | Meaning |
|---|---|
| Thermal expansion | The increase in size of a material when its temperature rises. |
| Internal energy | Sum of the kinetic and potential energies of the particles in a system. |
| Specific heat capacity | Energy needed per kilogram per degree Celsius of temperature rise. |
| Bimetallic strip | Two metals joined that bend when heated because they expand differently. |
| Capillary tube | A very narrow tube, as in a thermometer. |
Avoid these mistakes
1
Saying molecules get bigger when heated — the separation increases.
2
Using grams in ΔE = mcΔθ.
3
Confusing temperature with internal energy — temperature relates to average kinetic energy only.
4
Writing the unit of c as J/kg without the degree Celsius.
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