Heat: Paper 2 Answering Guide (Form 4 SPM Physics)

Paper 2 at a glance

• Section A: 8 structured items worth 60 marks, answer all

"Define" items from this chapter

One precise sentence each; the unit is part of the definition where there is one.

• 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).

"Explain" items from this chapter

Give the physics reason, not a description. Model answers in one breath:

• 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.

"Calculate" items from this chapter

Formula, substitution with units, answer with unit, and the trap examiners set for each one.

• 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) · Use the value of c given in the question, and keep temperature change (not absolute temperature) in °C.
• Q = mL, Specific latent heat, Q = heat energy (J); m = mass (kg); L = specific latent heat (J kg⁻¹) · During a change of state the temperature stays constant, so there is no θ term. Use the correct L (fusion for melting, vaporisation for boiling).
• 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) · Temperature must be in kelvin (K = °C + 273). Volume may be in any unit as long as both sides match.
• p₁V₁ = p₂V₂, Boyle's law, p₁ = initial pressure (Pa); V₁ = initial volume (m³); p₂ = final pressure (Pa); V₂ = final volume (m³) · Valid only at constant temperature for a fixed mass of gas. Pressure and volume are inversely proportional.
• 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) · Temperature must be in kelvin. Valid only at constant pressure for a fixed mass of gas.
• p₁ / T₁ = p₂ / T₂, Pressure law, p₁ = initial pressure (Pa); T₁ = initial absolute temperature (K); p₂ = final pressure (Pa); T₂ = final absolute temperature (K) · Temperature must be in kelvin. Valid only at constant volume for a fixed mass of gas.

Other command words

• Sketch, axes labelled with units, the shape that matters (curve vs straight line, intercept, origin), no plotted numbers needed.
• Compare, same feature, both cases, one line each, then the physics that links them.

Where the marks are in this chapter

The 4 content standards of Heat can each be asked as a definition, an explanation, a calculation or a diagram. We do not predict which will appear, prepare all of them.

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

A three-step answer routine

1. Count the marks: one idea per mark, so a 3-mark explain needs three physics statements.
2. Name the quantity and its symbol before you use it.
3. Re-read the stem for a hidden condition (constant temperature, uniform acceleration, smooth surface).

More Heat resources

• Chapter overview: Heat
• Revision Notes
• Common Mistakes
• Practice Questions
• 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)