Topic 4: Materials — Edexcel A-Level Physics
Test yourself on Topic 4: Materials with PEARSON EDEXCEL A-Level practice questions.
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Topic 4: Materials explained
The statement asks you to use the density equation, written in the specification as density = m/V, where m is mass and V is volume.
Read the full explanation
Rearranged, m = ρV and V = m/ρ. In a multiple-choice question you may be given a mass and a volume and asked for density, or given density and one other quantity and asked to find the third. Work in SI units: convert grams to kilograms (divide by 1000) and cm³ to m³ (multiply by 1 × 10⁻⁶), since 1 cm³ = 1 × 10⁻⁶ m³. For a regular solid, measure dimensions and compute V; for an irregular solid, use displacement. Check the magnitude: water has a density of about 1000 kg m⁻³, so an answer far from that for a watery material signals a unit slip.
Your focus
- Select and rearrange density = m/V to find mass, volume or density.
- Convert masses and volumes into SI units before substitution.
- Evaluate whether a computed density is physically reasonable.
Topic 4: Materials exam tips
Marking Points
- Recognises the equation as density = mass ÷ volume and selects the correct rearrangement for the quantity asked.
- Converts mass to kilograms and volume to cubic metres before substituting, using 1 cm³ = 1 × 10⁻⁶ m³.
- Substitutes values correctly and computes density in kg m⁻³ (or the requested unit) with appropriate significant figures.
- Checks the answer against a sensible magnitude, for example comparing with water at about 1000 kg m⁻³.
Examiner Tips
- 💡Write the equation and rearrangement down before substituting numbers, so the target quantity is clear.
- 💡Convert every quantity to SI units in a single step and note the conversion factor you used.
- 💡Estimate the expected order of magnitude first, then compare your computed answer with it.
Common Mistakes
- Leaving mass in grams while volume is in m³, giving a density 1000 times too large; the correction is to convert grams to kilograms first.
- Converting cm³ to m³ by dividing by 100 instead of multiplying by 1 × 10⁻⁶; the correction is to use the cubic conversion factor.
- Using the diameter of a sphere as its radius when computing volume; the correction is to halve the diameter before cubing.