SI units, prefixes and homogeneity
Watch the whole lecture free
Make a free account to watch every lecture to the end: 3 worked examples, 5 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
That was the teaching part. The rest of this lecture is free with an account: 3 worked examples, 5 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
No password needed now: we email you a link to set one. Already have an account? Sign in, then come back to this page.
The teaching part (1 min) is free to watch. A free account opens the whole lecture: 3 worked examples, 5 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- A number is not enough
- The base quantities
Read the transcript of the teaching part
Last time
Before we start: last time, in Errors, precision and combining uncertainties, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
A number is not enough
A student writes that a rod is forty long. Forty what? Centimetres, metres, miles? A physical quantity is a number and a unit, and every unit in physics is built from just seven base units.
The base quantities
Mass has the base unit kilogram, symbol kg. Length is measured in metres, and time in seconds. Electric current is measured in amperes, and thermodynamic temperature in kelvin. Amount of substance has the mole as its unit. Charge is not a base quantity: the coulomb is derived.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Derived units in SI base units · Prefixes and powers of ten · SI base quantities and units · What a physical quantity is · Derived units in SI base units.
The whole chapter: Physical Quantities and Units, Physical Quantities and Units.
Chapter 1.1: Physical quantities
- Scalars, vectors, adding and resolving 5 min
- SI units, prefixes and homogeneity 5 min
Also for A Level Physics 9702
Which topics come up most in A Level Physics 9702 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency.