2.0 Measurement I

This chapter introduces the basic skills of measuring physical quantities accurately. Measurement is the process of finding the size or amount of a physical quantity using standard instruments and units. Accurate measurement is very important in Physics because it helps us describe the world reliably and compare results.

2.1 Physical Quantities and SI Units

A physical quantity is anything that can be measured. There are two types:

• Base quantities (Fundamental quantities): These are the basic quantities from which all others are derived. There are seven base quantities in the SI system.
• Derived quantities: These are obtained by combining base quantities (e.g., by multiplication or division).

Base Quantities and Their SI Units

• Length — Symbol: l — SI Unit: metre (m)
• Mass — Symbol: m — SI Unit: kilogram (kg)
• Time — Symbol: t — SI Unit: second (s)
• Electric current — Symbol: I — SI Unit: ampere (A)
• Temperature — Symbol: T — SI Unit: kelvin (K)
• Amount of substance — Symbol: n — SI Unit: mole (mol)
• Luminous intensity — Symbol: Iv — SI Unit: candela (cd)

SI Units (Système Intern