Question

In a capillary tube water rises up to a certain height and the upward force due to surface tension balances the force of 7.5*10-4 N due to weight of water. If the surface tension of the water is 6*10-2 N/m then what will be the internal circumference of the capillary tube.
[Answer : 1.25 * 10-2 m ]

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Answer 1

Explanation:

Given In a capillary tube water rises up to a certain height and the upward force due to surface tension balances the force of 7.5*10-4 N due to weight of water. If the surface tension of the water is 6*10-2 N/m then what will be the internal circumference of the capillary tube.

• Total upward force by surface tension = weight of liquid and angle of contact is 0 degree
• Force upward = surface tension x 2 π R
•                       = 2 π R T  
• Now downward force by water is 7.5 x 10^-4 N and therefore F upward is 7.5 x 10^-4 N
• 2 π R T = 7.5 x 10^-4 N
• 2 π R x 6 x 10^-2 = 7.5 x 10^-4
• 2 π R = 7.5 x 10^-4 / 6 x 10^-2
•         = 1.25 x 10^-2 m

So circumference is 2 π R = 1.25 x 10^-2 m

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