Heat: Revision Notes (Form 4 SPM Physics)

What this chapter covers

• 4.1 Thermal Equilibrium
• 4.2 Specific Heat Capacity
• 4.3 Specific Latent Heat
• 4.4 Gas Laws

Key ideas explained

• Why the sea heats up slower than land, Water has a high specific heat capacity, so it needs a lot of heat to warm up and gives out a lot as it cools. That is why the sea warms and cools more slowly than sand.
• Why sweating cools you down, As sweat evaporates it takes latent heat from your skin to turn from liquid to vapour. Losing that heat is what leaves your skin feeling cooler.
• Why a pressure cooker cooks faster, Sealing the pot lets pressure build up, and higher pressure raises the boiling point of water. The food then cooks in hotter water and steam, so it is done sooner.

Formulas to memorise (none are given in the exam)

• Q = mcθ, Specific heat capacity, Q = heat energy (J); m = mass (kg); c = specific heat capacity (J kg⁻¹ °C⁻¹); θ = temperature change (°C)
• Q = mL, Specific latent heat, Q = heat energy (J); m = mass (kg); L = specific latent heat (J kg⁻¹)
• p₁V₁ / T₁ = p₂V₂ / T₂, General gas law, p₁ = initial pressure (Pa); V₁ = initial volume (m³); T₁ = initial absolute temperature (K); p₂ = final pressure (Pa); V₂ = final volume (m³); T₂ = final absolute temperature (K)
• p₁V₁ = p₂V₂, Boyle's law, p₁ = initial pressure (Pa); V₁ = initial volume (m³); p₂ = final pressure (Pa); V₂ = final volume (m³)
• V₁ / T₁ = V₂ / T₂, Charles's law, V₁ = initial volume (m³); T₁ = initial absolute temperature (K); V₂ = final volume (m³); T₂ = final absolute temperature (K)
• p₁ / T₁ = p₂ / T₂, Pressure law, p₁ = initial pressure (Pa); T₁ = initial absolute temperature (K); p₂ = final pressure (Pa); T₂ = final absolute temperature (K)

Experiments the DSKP names

• 4.2.3 · Determine the specific heat capacity of water and of aluminium
• 4.3.3 · Determine the specific latent heat of fusion of ice and of vaporisation of water
• 4.4.2 · Pressure–volume of a fixed mass of gas at constant temperature (Boyle's law)
• 4.4.3 · Volume–temperature of a fixed mass of gas at constant pressure (Charles's law)
• 4.4.4 · Pressure–temperature of a fixed mass of gas at constant volume (pressure law)

Terms you must define precisely

• Boyle's law, For a fixed mass of gas at constant temperature, the pressure is inversely proportional to its volume (pressure × volume = constant).
• Charles's law, For a fixed mass of gas at constant pressure, the volume is directly proportional to its absolute temperature.
• Pressure law, For a fixed mass of gas at constant volume, the pressure is directly proportional to its absolute temperature.
• Absolute zero, The lowest possible temperature, 0 K or about −273.15 °C, at which the particles of a substance have minimum kinetic energy.
• Absolute temperature scale, The temperature scale that begins at absolute zero and is measured in kelvin (K), where a change of 1 K equals a change of 1 °C.
• Temperature, A measure of the degree of hotness of a body, related to the average kinetic energy of its particles; measured in degrees Celsius (°C) or kelvin (K).
• Heat, The energy transferred between bodies because of a difference in temperature; a form of energy measured in joules (J).
• Thermal equilibrium, The state reached when two bodies in contact are at the same temperature, so there is no net transfer of heat between them.

A revision order that works

1. Rewrite every definition in one sentence with the correct unit; definitions are the cheapest marks in Paper 2.
2. Derive each formula once from its meaning, then practise rearranging it before substituting numbers.
3. For each experiment, write the manipulated, responding and constant variables from memory, then the graph you would plot.
4. Finish with a timed set of calculations with units on every line.
5. Read the 4 standards above and tick the ones you can already explain aloud without notes.

More Heat resources

• Chapter overview: Heat
• Common Mistakes
• Practice Questions
• Paper 2 Answering Guide
• Paper 3 Guide
• Key Terms
• Calculation practice sets

Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)