Relative Density

📚 Key Concepts

🔹 Real-Life Example

Jewellers use relative density (RD) to test gold purity. Pure gold has RD = 19.3, while 18-karat gold has lower RD due to other metals mixed in. Similarly, alcoholic beverages are tested using hydrometers that measure relative density — higher alcohol content means lower relative density.

🔹 Relative Density: The ratio of the density of a substance to the density of water at 4°C.

🧪 Important Formulas

🔸 Mathematical Formula

RD = Density of substance / Density of water
RD = ρ_substance / ρ_water

🔹 Key Properties

• No unit: RD is a dimensionless quantity
• Reference: Water at 4°C is the standard reference
• Numerical value: RD is equal to density in g/cm³ (if water’s density = 1 g/cm³)

🔹 Applications of Relative Density

• Purity checking: Gold, silver, and precious stones
• Quality control: Milk, honey, petroleum products
• Battery testing: Measures specific gravity of battery acid
• Brewing: Measures alcohol content in beverages

Lower RD indicates more impurities or different alloy composition.

🔹 Sample Values