IP Physics Notes (Upper Secondary, Year 3-4): 9) Thermal Physics
IP Physics Notes (Upper Secondary, Year 3-4): 9) Thermal Physics
Study guide//Updated 16 Jul 2026
Reviewed by
Chee Wei Jie·Academic Advisor (Physics)
Temperature scales, kinetic theory, gas laws (Boyle's, Charles' Law experiment), heat transfer, and specific heat/latent heat calculations for IP Physics.
Q: What does IP Physics Notes (Upper Secondary, Year 3-4): 9) Thermal Physics cover? A: Temperature scales, kinetic theory, heat transfer pathways, and specific heat/latent heat calculations for IP students.
Quick recap -- Temperature tracks particle kinetic energy, while heating changes the internal energy of matter through conduction, convection, or radiation. Quantify changes with specific heat and latent heat relations.
The core idea is simple: Heating changes internal energy; temperature tracks average particle kinetic energy.
Use it as a working check: Use conduction, convection, and radiation for transfer pathways. Use specific heat when temperature changes, and latent heat when state changes at constant temperature.
Then go one layer deeper: Work through the aluminium and phase-change examples to practise choosing Q=mcΔθ or Q=mℓ, then explaining the particle model behind the calculation.
For Integrated Programme students: Your current school materials, teacher instructions, and assessment scope take precedence because IP topic sequence and depth vary by school. This is an Eclat IP guide, not the O-Level / SEC G3 exam-track guide.
How this chapter applies
Eclat blended core: Marcus Pang combines the kinetic particle model, thermal processes, and thermal properties because IP questions often assess particle explanation, energy transfer, and calculation in one problem.
Eclat recap and extension: thermometer calibration and the gas-law relationships reinforce lower-secondary foundations and school-dependent IP depth. They are not a reason to treat every item as universal assessed scope.
2027 national comparison: this one Eclat chapter overlaps with K323 Topics 7, 8, and 9. The national exam map keeps them separate while Eclat deliberately teaches them together.
Check your school: confirm whether the current assessment includes thermometer calibration, gas laws, electrical heating experiments, or only the thermal core.
Temperature: measure of hotness; in the kinetic particle model, higher temperature corresponds to greater average particle kinetic energy. The SI base unit is kelvin (K).
Convert: TK=T∘C+273.15.
Thermometers rely on thermometric properties (e.g., expansion of liquids, emf in thermocouples, electrical resistance).
Calibration uses fixed points: ice point (0∘C), steam point (100∘C).
Kinetic Model of Matter
Solids: tightly packed, vibrate about fixed positions; strong intermolecular forces.
Liquids: particles slide past each other; weaker forces, definite volume but no fixed shape.
Gases: particles far apart, random motion, negligible forces.
Brownian motion evidences particle movement.
Gas behaviour:
At constant volume, increasing temperature raises pressure (particles strike walls harder and more often).
At constant pressure, raising temperature expands volume - this is Charles' Law (V∝T at constant pressure). See our Charles' Law experiment walkthrough for the full practical setup.
Boyle's law (Chapter 5) links pressure and volume at fixed temperature.
Gas-law setup checkpoint
Before substituting into a gas-law relationship, identify the quantity kept constant and convert temperature to kelvin. Gas-law proportionalities use absolute temperature, not degree Celsius readings.
Question cue
Quantity kept constant
Relationship to use
Common trap
"Fixed volume" or sealed rigid container
Volume
p∝T
Using ∘C directly for temperature.
"Constant pressure" or freely moving piston
Pressure
V∝T
Saying volume doubles when Celsius temperature doubles.
"Constant temperature" or slow compression
Temperature
pV=constant
Applying Charles' law when the question is about pressure and volume.
Graph of V against T for a gas
Pressure and amount of gas
Straight line when T is in kelvin
Extrapolating from a Celsius graph without converting the scale.
Worked check: a gas at constant pressure has volume 200cm3 at 27∘C. If it is heated to 57∘C, convert first:
T1=300 K,T2=330 K.
Since V∝T,
V2=200×300330=220cm3.
Misconception check: 57∘C is not "about twice as hot" as 27∘C for gas-law calculations. The absolute temperatures are 330K and 300K, so the volume increases by only 10%.
Transfer of Thermal Energy
Heat flows from higher to lower temperature regions.
Conduction: particle collisions/free electron diffusion in solids. Metals conduct well due to mobile electrons; insulators do not.
Convection: bulk fluid movement; heated regions expand, become less dense, and rise while cooler fluid sinks to replace them.
Radiation: emission of electromagnetic waves (mainly infrared); no medium required. Rate increases with higher surface temperature, larger surface area, and matte black surfaces.
When a question asks "which transfer process is involved?", start from the physical clue before naming the process.
Question clue
Likely process
Explanation to write
Heat moves through a metal rod or pan handle
Conduction
Faster particles and mobile electrons transfer energy through the solid without bulk movement of the solid.
Warm fluid rises and cooler fluid sinks to replace it
Convection
Heating lowers the fluid density, so the warmer region rises and sets up a convection current.
Heat crosses a vacuum or empty gap
Radiation
Infrared radiation transfers energy without needing particles between the source and receiver.
A black, dull surface heats or cools faster than a shiny surface
Radiation
Black, dull surfaces are better absorbers and emitters of infrared radiation.
A foam, plastic, air, or vacuum layer is used to reduce heat loss
Insulation by reducing one or more transfer paths
Name the blocked path: poor conduction through trapped air or foam, reduced convection when air cannot circulate, or reduced radiation from shiny surfaces.
Common trap: do not write "heat rises" as the full explanation. Hot fluids rise because they become less dense; radiation can transfer energy sideways or downward as well.
Internal Energy & Specific Heat Capacity
Internal energy = sum of microscopic kinetic + potential energies.
Heating a body raises internal energy; some energy changes kinetic (temperature rises), some potential (phase change).
Specific heat capacityc: energy required per kilogram per kelvin change, units J⋅kg−1⋅K−1.
Thermal energy change: Q=mcΔθ
Experimentally determine c using electrical heating: measure voltage V, current I, time t; equate VIt=mcΔθ
Electrical heating checkpoint
For specific heat capacity experiments, separate the electrical energy supplied from the useful thermal energy gained by the sample. The equation VIt=mcΔθ assumes that the electrical energy mostly heats the measured object.
Decision
What to write
Common trap
Energy supplied by heater
Use E=VIt, with V in volts, I in amperes, and t in seconds.
Using minutes directly for t.
Useful temperature change
Use Δθ=θfinal−θinitial.
Substituting the final temperature instead of the temperature rise.
Mass heated
Use the mass of the block or liquid being heated in kg.
Using grams with J⋅kg−1⋅K−1.
Heat loss check
Mention insulation, lid, stirring, and thermometer contact when evaluating accuracy.
Assuming every joule from the heater enters only the sample.
Worked check: a 0.50kg metal block is heated by a 6.0V, 2.0A heater for 300s, and its temperature rises by 8.0∘C. The electrical energy supplied is E=6.0×2.0×300=3600J, so
c=mΔθE=0.50×8.03600=900J⋅kg−1⋅K−1.
Misconception check: if heat is lost to the surroundings or the heater warms itself, VIt is larger than the useful energy gained by the sample. That usually makes the calculated c too large if the loss is ignored.
Worked Example: Heating Aluminium
A 0.80kg aluminium block (c=900J⋅kg−1⋅K−1) warms from 22∘C to 75∘C.
Q=mcΔθ=0.80×900×(75−22)=3.8×104J.
Change of State & Latent Heat
During melting/boiling, temperature stays constant while energy changes molecular potential energy.
Specific latent heatℓ: energy per kilogram needed for phase change at constant temperature.
Fusion: solid to liquid, ℓf.
Vaporisation: liquid to gas, ℓv.
Energy for phase change: Q=mℓ
Electrical method: VIt=mℓ (measure mass melted or evaporated).
Boiling vs Evaporation
Feature
Evaporation
Boiling
Occurs at
Any temperature
Fixed boiling point
Location
Surface only
Throughout liquid
Rate
Slow
Rapid
Temperature change
Causes cooling
Temperature constant
Energy source
Surroundings
Continuous heating
Cooling & Heating Curves
Plotting temperature vs time at constant heating/cooling power shows plateaus during phase changes.
Longer plateau at boiling because ℓv>ℓf for most substances.
Gradient in each sloped section inversely proportional to specific heat capacity in that state.
Curve-reading checkpoint
Read a heating or cooling curve by asking what stays constant first, then decide which energy equation applies.
Curve feature
What particles are doing
Equation cue
Common trap
Sloping section while heating
Particles gain average kinetic energy, so temperature rises.
Use Q=mcΔθ.
Using latent heat when the state has not changed.
Flat section while heating
Particles overcome attractive forces during a state change, so temperature stays constant.
Use Q=mℓ.
Saying no energy is absorbed because the thermometer reading is constant.
Steeper sloping section
Temperature changes faster for the same heating power.
Smaller heat capacity for the same mass and power.
Comparing gradients without checking that power and mass are the same.
Longer plateau
More energy is needed for that state change.
Larger latent heat or larger mass.
Assuming a longer plateau means a higher boiling point.
Worked check: if ice warms from −10∘C to 0∘C, melts at 0∘C, then the water warms to 20∘C, split the calculation into three parts: ice warming with Q=mcΔθ, melting with Q=mℓf, and water warming with Q=mcΔθ.
Misconception check: a constant-temperature plateau does not mean particles stop gaining energy. The added energy changes the arrangement and separation of particles instead of raising their average kinetic energy.
Key Takeaways
Temperature is a measure of average kinetic energy; Kelvin scale shifts Celsius by 273.15.
Conduction, convection, and radiation each dominate under different circumstances.
Use Q=mcΔθ for sensible heating and Q=mℓ for latent heating.
Cooling curves visualise internal energy shifts between kinetic and potential contributions.
Practice Quiz
Ready to check your understanding? Challenge yourself with multi-step MCQs and structured-response prompts targeting every concept in this chapter.
