This mini-lesson walks you through the whole of Edexcel Topic 1 — Key concepts of physics: the SI base units, the prefixes and powers of ten, converting between units, working to the right number of significant figures and in standard form, and how to select and apply physics equations.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.
Scientists worldwide measure with one shared system: SI units. A handful of base units are the building blocks — every other unit is derived by combining them.
Watch out: the kilogram is the SI base unit of mass — not the gram — even though it already carries the "kilo" prefix. The newton, joule, watt and pascal are derived units: they are built from base units (e.g. 1 N = 1 kg·m/s²).
Tap whether each unit is an SI base unit or a derived unit.
A prefix in front of a unit multiplies it by a power of ten. "kilo" means ×1000, "milli" means ÷1000, and so on. Climbing the ladder, each step changes the size of what you are measuring.
Common mix-up: a lower-case m means milli (×10⁻³) but a capital M means mega (×10⁶). They differ by a factor of a billion, so the case really matters.
Tap a prefix, then tap the matching power of ten.
Tap a prefix, then drop it into the box that says whether it makes the unit bigger or smaller.
To convert, decide whether you are going to a bigger unit (so the number gets smaller) or a smaller unit (so the number gets bigger), then multiply or divide by the right power of ten.
How many seconds are in 2 hours?
1 hour = 60 min, and 1 min = 60 s, so 1 hour = 60 × 60 = 3600 s.
2 hours = 2 × 3600 = 7200 s
Watch out: for an hours → seconds conversion you must multiply by 3600, not 60. Many marks are lost by stopping after one ×60.
Standard form writes any number as a digit between 1 and 10, multiplied by a power of ten. It keeps huge and tiny physics numbers tidy.
Watch out: the front number a must be at least 1 and below 10. Writing 45 × 10² is not proper standard form — it should be 4.5 × 10³.
Significant figures (s.f.) are the meaningful digits in a number, counted from the first non-zero digit. Your answer should not look more precise than the data you were given.
Round 47 853 to 2 significant figures.
The first two figures are 4 and 7. The next digit is 8 (≥5), so round up: 48 000.
Exam tip: if a question gives data to 2 s.f., give your final answer to about 2 s.f. too — don't copy out every digit your calculator shows.
Topic 1 also expects you to recall and select the right physics equation and apply it correctly. The reliable routine is: write the equation, substitute the numbers in SI units, then calculate.
Golden rule: convert every value to SI base units before you substitute. Put minutes into seconds, kilometres into metres and grams into kilograms first — otherwise the answer's units will be wrong.
A toy car covers 600 cm in 4 s. Average speed = distance ÷ time.
Convert: 600 cm = 600 ÷ 100 = 6 m.
speed = 6 ÷ 4 = 1.5 m/s
SI base units: metre (m), kilogram (kg), second (s), ampere (A), kelvin (K)
Derived units: newton (N), joule (J), watt (W), pascal (Pa)
Prefixes: G 10⁹ · M 10⁶ · k 10³ · c 10⁻² · m 10⁻³ · µ 10⁻⁶ · n 10⁻⁹
Converting: 1 hour = 3600 s · 1 km = 1000 m
Standard form: a × 10ⁿ with 1 ≤ a < 10
Significant figures: count from the first non-zero digit; match the data's precision
Using equations: convert to SI units → substitute → calculate
You've covered the whole of Edexcel Topic 1 — units, prefixes, conversions, standard form, significant figures and applying equations. Press Finish to see your score.
You've worked through Key Concepts of Physics for Edexcel GCSE Physics. 🎉
Your stars: 0 / 0
Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.