A vertical clean glass tube of uniform bore is used, as a piezometer to measure the pressure of liquid at a point. The liquid has a specific weight of 15 kN/m3 and a surface tension of 0.06 N/m in contact with air. If for the liquid, the angle of contact with glass is zero and the capillary rise in the tube is not to exceed 2 mm, what is the required minimum diameter of the tube?
a. 6 mm b. 8 mm
c. 10 mm d. 12 mm