Are formulas given in the exam?

No. You must recall SPM Physics formulas.

Is a formula sheet given for these calculations?

No. SPM Physics (4531) provides no formula sheet, recall each formula and write units on every line.

What does the medium band mean?

Mid-level items usually need one rearrangement and a unit conversion.

Can a tutor mark my working?

Yes, in a one-to-one lesson the teacher checks each line and fixes the exact step that loses marks. From RM50/hr, paid trial available.

Heat Calculations (Medium), SPM Physics

How to approach

These need a rearrangement or two steps, often finding one quantity before the one asked for.

The method

List what is given, with units.
Choose the formula and rearrange for the unknown.
Substitute with units on every line.
Round to the correct significant figures.

Worked examples

Specific heat capacity

Q = mcθ

Find the heat needed to raise 2 kg of water (c = 4200 J kg⁻¹ °C⁻¹) by 30 °C. Q = mcθ = 2 × 4200 × 30 = 252000 J = 2.52 × 10⁵ J.

Specific latent heat

Q = mL

Find the heat to melt m = 0.5 kg of ice (L = 3.34 × 10⁵ J kg⁻¹). Q = mL = 0.5 × 3.34 × 10⁵ = 1.67 × 10⁵ J.

General gas law

p₁V₁ / T₁ = p₂V₂ / T₂

Gas at p₁ = 1.0 × 10⁵ Pa, V₁ = 2.0 L, T₁ = 300 K is changed to p₂ = 2.0 × 10⁵ Pa, T₂ = 600 K. V₂ = p₁V₁T₂ / (T₁p₂) = (1.0 × 10⁵ × 2.0 × 600) / (300 × 2.0 × 10⁵) = 2.0 L.

Boyle's law

p₁V₁ = p₂V₂

Gas at p₁ = 100 kPa, V₁ = 500 cm³ is compressed to V₂ = 200 cm³ at constant temperature. p₂ = p₁V₁ / V₂ = (100 × 500) / 200 = 250 kPa.

Charles's law

V₁ / T₁ = V₂ / T₂

Gas of volume V₁ = 300 cm³ at T₁ = 300 K is heated to T₂ = 400 K at constant pressure. V₂ = V₁T₂ / T₁ = (300 × 400) / 300 = 400 cm³.

Pressure law

p₁ / T₁ = p₂ / T₂

Gas at p₁ = 100 kPa, T₁ = 300 K is heated to T₂ = 450 K at constant volume. p₂ = p₁T₂ / T₁ = (100 × 450) / 300 = 150 kPa.

Where marks are lost

Skipping units, rounding too early, and writing only the final answer (which loses method marks in Paper 2).

Practise these

Try each formula above with your own numbers, showing every line. Bring anything you get stuck on to a one-to-one lesson.

Formulas you use for Heat calculations

These mid-level problems draw on the 6 relationships in Heat. None is printed in the exam, so recall each and write its symbols with units before substituting:

Q = mcθ, Specific heat capacity
Q = mL, Specific latent heat
p₁V₁ / T₁ = p₂V₂ / T₂, General gas law
p₁V₁ = p₂V₂, Boyle's law
V₁ / T₁ = V₂ / T₂, Charles's law
p₁ / T₁ = p₂ / T₂, Pressure law

A worked example, with units on every line

Using p₁V₁ = p₂V₂ (p₁ = initial pressure (Pa); V₁ = initial volume (m³); p₂ = final pressure (Pa); V₂ = final volume (m³)):

Gas at p₁ = 100 kPa, V₁ = 500 cm³ is compressed to V₂ = 200 cm³ at constant temperature.
p₂ = p₁V₁ / V₂ = (100 × 500) / 200 = 250 kPa.

Where the marks are, and the common mistakes

In Paper 2, calculation marks are awarded line by line: the formula, the substitution with units, and the final answer with its unit and sensible significant figures. Watch this trap: Valid only at constant temperature for a fixed mass of gas.

Pressure and volume are inversely proportional. For mid-level items, expect one rearrangement and a unit conversion.

Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)

Written by the spmphysics.com.my editorial team.· Updated 5 Sept 2026