Question

A U tube contains water and methylated spirit separated by mercury. The mercury columns in the two arms are at the same level with 10 cm of water in one arm and 12.5 cm of spirit in the other as shown in figure. The relative density of the spirit is :

• A. 0.6
• B. 0.8
• C. 1
• D. 1.25

Answer 1

The correct option is B 0.8

Refer figure. As the mercury columns in the two arms of U tube are at the same level, therefore
Pressure due to water = Pressure due to spirit column
$P_o+{\rho }_w{h}_{w}g-{\rho }_s{h}_{s}g=P_o$

${\rho }_s=\frac{h_w}{h_s}{\rho }_w$
$\therefore$ Relative density of spirit

= $\frac{{\rho }_s}{{\rho }_w}=\frac{h_w}{h_s}=\frac{10cm}{12.5cm}=0.8$