What is a Physical Quantity? (Class 11 Physics)

A Physical Quantity is any physical property of a material, object, or phenomenon that can be accurately measured and quantified with a number.

To perfectly describe a physical quantity, you need two things:

1. Magnitude (The numerical value/number).
2. Unit (The standard of measurement). Example: If you say a boy's mass is '50 kg', the mass is the physical quantity, '50' is the magnitude, and 'kg' is the unit. (Just saying '50' is meaningless).

In physics, all quantities are strictly divided into two main categories:

1. Fundamental (Base) Quantities: These are entirely independent quantities that cannot be derived from any other quantity. There are exactly 7 fundamental quantities in the SI system:

• Mass (Kilogram)
• Length (Meter)
• Time (Second)
• Electric Current (Ampere)
• Temperature (Kelvin)
• Luminous Intensity (Candela)
• Amount of Substance (Mole)

2. Derived Quantities: These are complex quantities that are created by multiplying or dividing the fundamental quantities.

• Example 1: Area (Length $\times$ Length = m²).
• Example 2: Velocity (Length / Time = m/s).
• Example 3: Force (Mass $\times$ Acceleration = Newton).