Density of a substance is defined as the ratio of its mass to its volume.
Density of a liquid = Mass / Volume
Density of water = 1 g/cm3 or l03kg/m3
It is scalar quantity and its dimensional formula is [ML-3].
Relative density of a substance is defined as the ratio of its density to the density of water at
4°C,
Relative density = Density of substance / Density of water at 4°C
= Weight of substance in air / Loss of weight in water
Relative density also known as specific gravity has no unit, no dimensions.
For a solid body, density of body = density of substance
While for a hollow body, density of body is lesser than that of Substance.
When immiscible liquids of different densities are poured in a container, the liquid of highest density will be at the bottom while, that of lowest density at the top and interfaces will be plane.
Density of a Mixture of Substances
When two liquids of mass m1 and m2 having density p1 and p2 are mixed together then density of mixture is
p = m1 + m2 / (m1 /p1) + (m2 + p2)
= p1p2 (m1 + m2) / (m1p2 + m2p1)
When two liquids of same mass m but of different densities p1 and p2 are mixed together then density of mixture is
p = 2p1 p2 / p1 + p2
When two liquids of same volume V but of different densities p1 and p2 are mixed together then density of mixture is
p = p1 + p2 / 2
Density of a liquid varies with pressure
p = p0 [1 + Δp / K]
Where, p0 = initial density of the liquid, K = bulk modulus of elasticity of the liquid and Δp = change in pressure
