SI Base Quantities and Base Units
An SI base unit is the conventionally chosen reference unit for one of the seven base quantities; a derived unit is an algebraic product of powers of base units defined by a quantity equation.
Why this shows up in the exam
Checking laboratory unit labels · Building coherent derived units · Interpreting data sheets across disciplines
Learn the idea
Seven SI base quantities provide independent reference units from which coherent derived units are built. Treat the base units as an alphabet: metre, kilogram, second, ampere, kelvin, mole, and candela combine to spell every coherent SI derived unit.
🧠 Memory hook: Base quantities are the seven independent letters of SI.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- {L,M,T,I,Theta,N,J} — dimension symbols for length, mass, time, current, temperature, amount, and luminous intensity
- m, kg, s, A, K, mol, cd — the seven SI base-unit symbols
How to approach it
- 1Identify the physical quantity
- 2Expand any named derived unit
- 3Reduce it to the seven SI bases
Common slip-ups that cost marks
- •Treating radian as an eighth base unit
- •Using gram instead of kilogram as the SI mass base unit
- •Confusing a quantity symbol with its unit symbol
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A quantity Q is defined as Q = force^1 / speed^2. Which dimensional formula represents Q?
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