recall the following SI base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K)

SI Base Quantities and Their Units

In the International System of Units (SI) every physical quantity is expressed in terms of a set of base quantities. For the A‑Level Physics syllabus the following five base quantities are essential to remember.

List of SI Base Quantities

• Mass
• Length
• Time
• Electric current
• Thermodynamic temperature

Corresponding SI Units

Why These Units Matter

All other derived units used in physics are built from these base units. For example, the unit of force, the newton (N), is defined as:

\$\text{N} = \text{kg}\,\text{m}\,\text{s}^{-2}\$

Understanding the base units therefore allows you to decompose any derived unit back to its fundamental components.

Quick Recall Exercise

1. Write the SI unit for each of the five base quantities without looking at the table.
2. Express the unit of energy (joule) in terms of the base units.
3. State the relationship between the ampere and the coulomb.

Answers can be checked against the following summary.

Summary of Key Points

• Mass → kilogram (kg)
• Length → metre (m)
• Time → second (s)
• Current → ampere (A)
• Temperature → kelvin (K)