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Edexcel IGCSE Physics revision

Solids, liquids and gases units questions

Recognise density and pressure units, convert temperatures when needed, and read physical quantities accurately from graphs.

Edexcel IGCSE Physics Subtopic 5.a

Solids, liquids and gases units syllabus

Questions on solids, liquids and gases units can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

  • 5.1 use the following units: degree Celsius (°C), Kelvin (K), joule (J), kilogram (kg), kilogram/metre³ (kg/m³), metre (m), metre² (m²), metre³ (m³), metre/second (m/s), metre/second² (m/s²), newton (N) and pascal (Pa)
  • 5.2P use the following unit: joules/kilogram degree Celsius (J/kg °C)

How to answer solids, liquids and gases units questions

  1. Write the unit symbol exactly and distinguish quantities that use similar-looking units.
  2. Convert prefixes and compound units before substituting values into an equation.
  3. Check that the unit of the final answer matches the quantity asked for.
  4. Use the context of a diagram or calculation to reject units with the wrong dimensions.

Solids, liquids and gases units example questions and worked answers

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

Example 1: Choosing the unit of density

January 2012 · Paper 1P · Question 2(b)

Question 1

A student measures the density of water.
She uses a measuring cylinder and an electronic balance.

Photograph of a measuring cylinder and an electronic balance.

A correct unit for density is

A   g/cm
B   kg/cm
C   g/cm2
D   g/cm3

Final answer

D — g/cm3

Mark scheme points

  1. M1 Select D: g/cm3.

Explanation

Density is mass divided by volume. Since volume is measured in cubic centimetres, a suitable density unit is grams per cubic centimetre, g/cm3.

Common mistakes

  • Do not use cm or cm2: density uses a volume unit, so the length unit must be cubed.

Example 2: Reading gas-particle speed from a graph

January 2021 · Paper 1P · Question 8(d)(i)

Question 2

A student uses a computer simulation to investigate the motion of particles in a gas.

He records the pressure of the gas and the mean speed of the particles in the gas at different temperatures.

The graphs show his results.

Graph 1: pressure against temperature, with a rising straight line. Graph 2: mean particle speed against temperature, with a rising curve; the reading at 100 °C is about 520 m/s.

The student then calculates the kinetic energy of a single gas particle at each temperature.

Using the curve of best fit on graph 2, determine the mean speed of a gas particle when the gas temperature is 100°C.

mean speed = ________ m/s

Final answer

At 100°C, the mean speed is approximately 520 m/s.

Mark scheme points

  1. M1 Read a mean speed in the range 520–525 m/s from the curve of best fit on Graph 2.

Explanation

Find 100°C on the horizontal axis of Graph 2, then read the corresponding vertical value where it meets the curve of best fit. This gives a mean speed of about 520 m/s.

Common mistakes

  • The examiner report says this graph-reading mark was usually awarded. Read the value from Graph 2 at 100°C and check the vertical-axis scale carefully.

Practise Solids, liquids and gases units questions

Build a focused practice set from this part of the Edexcel IGCSE Physics syllabus.

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