Explain why it is important to use the correct SI unit when recording a measurement, and state the SI unit for each of the following: energy, electric charge, and pressure.

Edexcel GCSE Physics (1PH0) — 1.1 Key concepts of physics · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A student records the speed of a car as '30' without writing any unit. Another student records the same speed as '30 m/s'.

Model answer (4 marks)

Using the correct SI unit gives the measurement meaning and allows comparison with other data.
Energy: joule (J)
Electric charge: coulomb (C)
Pressure: pascal (Pa)

Examiner tips

Mention that a unit gives context and comparability; list the three SI units exactly; keep answer concise to fit 4 marks

Common mistakes

Omitting the unit or writing a non‑SI unit; writing the unit in the wrong form (e.g. 'Joule' instead of 'J'); forgetting to list all three units

Mark scheme (4 marks)

Without a unit (or with an incorrect unit), a measurement has no meaning / cannot be understood / cannot be compared by other scientists
The SI unit for energy is the joule (J)
The SI unit for electric charge is the coulomb (C)
The SI unit for pressure is the pascal (Pa)

Key terms in this question

SI unit · energy · electric charge · pressure