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what is relative density?explain with examples
The relative density (R.D.) of a substance is the ratio of the density of the substance to the density of water at 4 0C.
i.e., R.D = Density of substance/Density of water at 4 0C
              = Mass of unit volume of substance/Mass of unit volume of water at 4 0C
              = Mass of a certain volume of substance / Mass of same volume of water at 40C
Relative density of a substance is also defined as the ratio of the mass of substance to the mass of an equal volume of water at 40C.
Since relative density is a pure ratio,it has no unit.

In C.G.S system, the density of water at 40C is 1 gcm-3,therefore ,the relative density of a substance is equal to the numerical value of density of that substance.Thus
R.D = Density of substance in g cm-3/1.0 g cm-3
In S.I. system , the density of water at  4 0C is 1000 kg m-3,hence relative density 
R.D = Density of the substance in kg m-3/1000 kg m-3
Examples :
The density of copper is 8.9 g cm-3,its R.D is 8.9 .
The R.D of a silver is 10.8, its density in CGS unit is 10.8 g cm-3 and 
in S.I. unit is 10.8 x 103  kg m-3


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