Which of the following units is not fundamental?

Analyze the question You are asked to find the unit that is NOT a fundamental (base) SI unit, meaning it is a derived unit.

Explain the concept The SI system has seven fundamental (base) units:

| Quantity | Unit | |---|---| | Length | metre (m) | | Mass | kilogram (kg) | | Time | second (s) | | Electric current | ampere (A) | | Temperature | kelvin (K) | | Amount of substance | mole (mol) | | Luminous intensity | candela (cd) |

Any other unit is a derived unit, formed by combining base units.

Solution

• A. Metre is the base unit of length, so it is fundamental.
• B. Kilogram is the base unit of mass, so it is fundamental.
• C. Joule is the unit of energy or work. Since work = force × distance: J = N·m = (kg·m/s²)·m = kg·m²·s⁻² It is built from kilogram, metre and second, so it is derived.
• D. Candela is the base unit of luminous intensity, so it is fundamental.

Answer: The joule is not fundamental.

Tip: Memorise the seven base units with a phrase like "My Kind Sister Always Keeps Money Close" (metre, kilogram, second, ampere, kelvin, mole, candela). If a unit is not on the list, such as newton, joule, watt, pascal, hertz or coulomb, it is derived.