The surface tension of water was determined in a laboratory by using the drop weight method. 100 drops were released from a burette the inner diameter of whose opening is 1.8 mm

0.06563 N/m

The percentage difference between the calculated and tabulated value of water surface tension is 9.78%

Explanation:

Solution:-

- Surface tension is the ability of any fluid to resist any external force due to cohesive nature of the fluid molecules.

- Surface tension ( γ ) is defined as the force imparted per unit length on the fluid.

                          γ = F / L

Where,

             F: Force

             L: The length over which force is felt

- The mass ( M = 3.78g ) of ( n = 100 ) water droplets are carefully burette. We need to determine the mass of a single droplet as follows:

                        m = M / n

                        m = 3.78 / 100

                        m = 0.0378 g        

- Assuming the distance over which the drop falls is negligible and resistive forces are negligible. Then the only force acting on the droplet is due to gravity ( Weight of the droplet ):

                       F = m*g

                       F = 0.0378*9.81*10^-3

                       F = 0.000370818 N      

- The length over which the force is felt can be modeled into a circular patch with diameter ( d ) = equal to the diameter ( d ) of the single water drop. The length ( L ) is defined as the circumference of the patch:

                       L = π*d

                       L = π*( 0.0018 )

                       L = 0.00565 m

- The surface tension would be:

                       γ = F / L

                       γ = 0.000370818 / 0.00565

                       γ = 0.06563 N / m

- The given value of water's surface tension is given as follows:

                      γa = 0.07275 N/m

- To compare the two values we will determine the percentage difference between the value evaluated  and tabulated value as follows:

                   % 

- The percentage difference ( 9.78% ) between the two values is within  practical limits of 10%. Hence, the calculated can be accepted.

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