Question

A droplet of water weighing 0.2 grams is placed on the surface of a perfectly clean glass plate. The diameter of the droplet is measured to be 5 mm. Calculate the surface tension of water in dynes/cm.

Answer 1

To calculate the surface tension of water, we can use the formula for the capillary rise method:Surface tension    =  hgR  / 2where h is the height of the water droplet,  is the density of water, g is the acceleration due to gravity, and R is the radius of the droplet.First, we need to find the volume of the water droplet:Weight = Volume  Density0.2 g = Volume  1 g/cmVolume = 0.2 cmNext, we can find the radius of the droplet:Diameter = 5 mm = 0.5 cmRadius  R  = Diameter / 2 = 0.5 cm / 2 = 0.25 cmNow, we can find the height of the droplet using the formula for the volume of a sphere:Volume =  4/3 R0.2 cm =  4/3  0.25 cm 0.2 cm =  4/3  0.015625 cm 0.2 cm /  4/3  = 0.015625 cmh = 0.015625 cm / 0.015625 cmh = 1 cmNow we can calculate the surface tension using the capillary rise method formula: =  hgR  / 2 =  1 cm  1 g/cm  980 cm/s  0.25 cm  / 2 =  245 dynes/cm  / 2 = 122.5 dynes/cmThe surface tension of water in this case is approximately 122.5 dynes/cm.