Describe what is meant by a prefix in physics and explain why prefixes are useful when measuring physical quantities. Give two examples of prefixes to support your answer.

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

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

Model answer (4 marks)

A prefix is a word or symbol placed before a unit that represents a power of ten multiplier.
Prefixes are useful because they avoid writing very large or very small numbers and make values easier to read and record.
For example, kilo (k) = ×10³.
Another example is milli (m) = ×10⁻³.

Examiner tips

Use the exact wording "prefix is a word or symbol placed before a unit that represents a power of ten multiplier" to secure the first point. Show the two examples with both the symbol and the multiplier to gain the remaining points. Keep the answer concise – no extra sentences are needed.

Common mistakes

Writing a prefix without its symbol or multiplier. Using a non‑SI prefix (e.g. "centi" is fine, but "deci" is less common in the mark scheme). Adding unnecessary explanation or restating the question.

Mark scheme (4 marks)

A prefix is a word or symbol placed before a unit that represents a power of ten multiplier (scaling factor).
Prefixes are useful because they avoid writing very large or very small numbers / make values easier to read and record.
Correct first example of a prefix with its symbol and multiplier, e.g. kilo (k) = × 10³, or mega (M) = × 10⁶, or milli (m) = × 10⁻³, or nano (n) = × 10⁻⁹, etc.
Correct second, different example of a prefix with its symbol and multiplier.

Key terms in this question

prefix