h = Difference of mercury level in the U-tube
y = Distance of the centre of B, from the mercury level in the right limb
x = Distance of the centre of A, from the mercury level in the right limb
ρ
1 = Density of liquid at A
ρ
2 = Density of liquid at B
ρ
g = Density of heavy liquid or mercury
Hence the difference in the pressure between A and B, when A and B are at different level is given by,
P
A – P
B = h × g × (ρ
g – ρ
1) +ρ
2gY – ρ
1gX
Hence the difference in the pressure between A and B, when A and B are at same level is given by,
P
A – P
B = g × h × (ρ
g – ρ
1)
2) Inverted U-tube differential manometerIt consists of an inverted U-tube, containing light liquid. It is used for measuring difference of low pressures
Calculation:
Given,Oil specific gravity = 0.9
Difference in mercury level = 15 cm = 0.15 m
ρ
hg = 13600 kg/m
3 ρ
oil = 0.9 × 1000 = 900 kg/m
3P
A + [900 × g × (Y + 0.15)] = P
B + (900 × g × Y) + [0.15 × g × 13600]
P
A - P
B = (13600 × g × 0.15) - (900 × g × 0.15)
PA - PB = 18688 N/m
2