Q. The capillary rise in the glass tube is not to exceed 0.2 mm of water. Determine its minimum size, given that surface tension for water in contact with air = 0.0725 N/m.
SOLUTION:
Capillary rise, h = 0.2mm = 0.2 * 10³ m
Surface tension σ = 0.0725N / m
Let dia. of tube = d
The angle for water =0
Density (P) for water = 1000kg / (m ^ 3)
Using equation, we get
h=4σ/p×g×d
= (4 * 0.0725)/(1000 * 9.81d)
d = (4 * 0.0725)/(1000 * 9.81 * 2 * 10-³)
= 0.148m = 14.8cm Ans
Thus minimum diameter of the tube should be 14.8 сm.
Q. Find out the minimum size of glass tube that can be used to measure water level if the capillary rise in the tube is to be restricted to 2 mm. Consider surface tension of water in contact with air is 0.73575 N/m
SOLUTION:
Given:
Capillary rise,h = 2 mm = 2 * 10-³m
Surface tension,σ = 0.073575N / m
Let dia. of tube = d
The angle for water = 0
The density for water, ρ = 1000kg / (m³)
Using equation, we get
h = (4σ)/(ρ×g×d) (or) 2 * 10-³
= (4 * 0.073575)/(1000 * 9.81* d)
d = (4 * 0.073575)/(1000 * 9.81 * 2 * 10-³)
= 0.015m = 1.5cm Ans.
Thus minimum diameter of the tube should be 1.5 cm
