Which of the following units is derived?

Analyze the question The question asks which unit is a derived unit. Physical quantities are measured in either fundamental (base) units or derived units.

Explain the concept

• Fundamental (base) units are the SI units that are defined independently. They are: • metre (m) for length • kilogram (kg) for mass • second (s) for time • ampere (A) for electric current • kelvin (K) for temperature • mole (mol) for amount of substance • candela (cd) for luminous intensity
• Derived units are formed by combining base units through multiplication or division.

Solution Check each option:

• A. kg is the base unit of mass, so it is fundamental.
• B. m is the base unit of length, so it is fundamental.
• C. K is the base unit of temperature, so it is fundamental.
• D. N (newton) is the unit of force. From Newton's second law:

F = ma

so 1 N = 1 kg × 1 m/s² = 1 kg·m·s⁻²

The newton is built from kg, m and s, so it is a derived unit.

Answer: The correct option is D (N).

Exam tip Memorise the 7 base units (m, kg, s, A, K, mol, cd). If a unit is not on that list, it is derived. Other common derived units are the joule (J), watt (W), pascal (Pa), and hertz (Hz).