SI base unit
One of seven fundamental units of measurement in the International System of Units that cannot be derived from other units. SI base units include the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). All other SI units are derived combinations of these base units.
Real World
The kilogram was redefined in 2019 using the Planck constant rather than a physical platinum-iridium cylinder stored in Paris, ensuring every laboratory worldwide can reproduce the exact same standard independently.
Exam Focus
Memorise all seven SI base units and their symbols — questions often ask you to express derived units in base units.
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