A circular ring of radius 7cm is supported horizontally from the pan of a balance, so that it comes in contact with the water in a glass vessel. What force will be required to detach it from the surface of water? (Surface tention of water = 0.072N//m.)

A circular ring of radius 7cm is supported horizontally from the pan o

1.	A circular ring of radius 7cm is supported horizontally from the pan of a balance, so that it comes in contact with the water in a glass vessel. What force will be required to detach it from the surface of water? (Surface tention of water = 0.072N//m.)
Answer» Solution :NEGLECTING the thickness of the ring, the net downward force on the inner and OUTER circumference of the ring due to surface TENSION = `Sxx2pi(R+R)=Sxx4piR`. `S=0.072N//m, R=7cm=7xx10^(-2)m`. The vertical force required to detach it from the water surface is `F=Sxx4piR` `=0.072xx4xx(22)/(7)xx10^(-2)=6.336xx10^(-2)N`.