Question

Describe how can we find the relative density of an unknown liquid using Archimedes’ principle? [$4\text{marks}$]

Answer 1

Relative density of a substance is the ratio of the density of that substance to the density of water at 4℃. Archimedes’ principle can be used to perform an experiment that measures the weight of the liquid that is displaces by a body and weight of water displaced by the same body. [$1\text{mark}$]
The difference of weight of a body in air and the weight of a body in liquid gives the weight of the liquid displaced by the body.
To find the weight of the water displaced by the body, the difference of the weight of the body in air and weight of the body in water should be known
$W_1$ = weight of the body in air
$W_2$ = weight of the body when immersed in liquid
$W_3$ = weight of the body when immersed in water.
Hence, using the Archimedes’ principle the relative density can be found using the formula:

Relative density of liquid = $\frac{\text{Weight of the body in air – Weight of the body in liquid}}{\text{Weight of the body in air − Weight of the body in water}}$
$\frac{W_1-W_2}{W_1-W_3}$ [$3\text{marks}$]