Relative Density

The density of a substance is defined as mass of a unit volume. The unit of density is kilogram per metre cube (kg m^-3). It is also known as specific gravity.

Relative Density = Density of substance/ Density of water

Density of water: At 4°C (39.2°F)

= 1000 kg/m³ (or 1 g/cm³)

It is different for different substances. Ex- the density of gold is 19300 kg m^-3 while that of water is 1000 kg m^-3. The density of a given sample of a substance can help us to determine its purity.

Since the relative density is a ratio of similar quantities, it has no unit.

Example:- Relative density of silver is 10.8. The density of water is 10³ kg m^-3. What is the density of silver in SI unit?

Solution: Relative density of silver = 10.8

Relative density = Density of silver/Density of water

Density of silver = Relative density of silver × density of water

= 10.8 × 10³ kg m^-3.