Question

What is the SI unit of density?
(A) $g\,c{{m}^{-3}}$
(B) $g\,{{m}^{-3}}$
(C) $Kg\,{{m}^{-3}}$
(D) $Kg\,c{{m}^{-3}}$

Answer 1

Hint: Density is defined as the ratio of mass of a substance to its volume. It is the measurement of compactness of mass in a substance or an object. SI units are official internationally accepted units for the fundamental physical quantities.

Complete step by step answer:
Let’s look at the answer:
Density is the ratio of total mass of an object to its total volume. Since, it is a ratio of two physical quantities, therefore its unit will depend on the units of the two physical quantities.

Let’s see what the SI units of mass and volume are:
i) The SI unit of mass is kilogram. It is represented by the symbol Kg. 1 Kg is defined as the mass of the particular international prototype made of platinum-iridium and kept at the International Bureau of Weights and Measures.

ii) The SI unit of volume is cubic metre (${{m}^{-3}}$). Metre is actually the SI unit of length. Since, volume is measured using length, therefore, the unit of volume is derived from length.
So, we have found that the SI unit of density is kilogram per cubic metre. It is represented as Kg${{m}^{-3}}$.

Hence, the answer of the given question is option (C).

Note: Density is an intensive property, that is, it doesn’t depend on the amount of substance. The other popular units of density which is generally used in calculations is g$c{{m}^{-3}}$. It is the cgs unit of density.