Pressure in Liquid – The U-Tube

  1. Usually, a U-tube is used to compare and measure the density of liquids.
  2. The density of the 2 liquids is related by the equation:
    h1ρ1 = h2ρ2


Figure above shows a U-tube filled with water and liquid P. Liquid P is insoluble in water. Given that the density of water is 1000kg/m³, find the density of liquid P.

h1 = 10cm
h2 = 12 cm
ρ1 = 1000kg/m³
ρ2 = ?

h1ρ1 = h2ρ2
(10)(1000)=(12) ρ2
ρ2 = 10000/12

The density of liquid P = 833 kg/m³


The diagram shows a U-tube filled with two types of liquid, X and Y which are not mixable. If the density of liquid X and liquid Y are 1200 kg/m³ and 800 kg/m³ respectively, find the value of h.

h1 = 10cm
h2 = h
ρ1 = 800kg/m³
ρ2 = 1200kg/m³

h1ρ1 = h2ρ2
h= 12000/800
h =15cm