Determine height h of oil in the U tube as shown in fig. Density of oil `=0.9 g//c c`, Density of liquid is `1.6 g//c c` and density of mercury. `= 13.6 g//c`.

Explanation

In equilibrium state, the pressure of liquid at the same level must be equal. Taking pressure at level C in both arms of U tube, we have
Pressure due to h cm of oil + pressure due to `(20-h)` cm of mercury
= pressure of 20 cm of liquid
i.e., `h xx 0.9 xx g + (20-h) xx 13.6 xxg`
`=20 xx 1.6 xx`
or `0.9h + 272 - 13.6h = 32`
or `12.7 h = 240 or h=(240)/(12.7) = 18.9 cm`.