A circular ring is cut from a platinum tube of 8.5 cm iknternal diameter nad 8.7 cm external diameter and supported horizontally from the pan of a balance, and supported horizontally from the pan of a balance, so that it comes in contact with the water in a glass vessel. If an extra weight of 3.97 g, is required to pull it away from water, calculate the surface tension of water.

A circular ring is cut from a platinum tube of 8.5 cm iknternal diamet

1.	A circular ring is cut from a platinum tube of 8.5 cm iknternal diameter nad 8.7 cm external diameter and supported horizontally from the pan of a balance, and supported horizontally from the pan of a balance, so that it comes in contact with the water in a glass vessel. If an extra weight of 3.97 g, is required to pull it away from water, calculate the surface tension of water.
Answer» Solution :When the ring is supported horizonally so that it COMES in CONTACT with water, there will be downward force due to surface tension. Downward pull on the inner circumference of the ring `2piR_(1)xxS` where `R_(1)` is the internal radius. Dowward pull on th outer circumference of the ring `=2piR_(2)xxS` where `R_(2)` is the external radius. Total downward pull or force on the ring due to surface tension `=sxx2pi(R_(1)+R_(2))` If m is the mass of the extra load requried to pull it AWAY, the load = MG so that `mg=Sxx2pi(R_(1)+R_(2))` `S=(mg)/(2pi(R_(1)+R_(2)))` `m=3.97g=3.97xx10^(-3)kg, g=9.8m//s^(2)` `R_(1)=8.5/2cm=4.25xx10^(-2)m` `R_(2)=8.7/2cm=4.35xx10^(-2)m` `S=(3.9xx10^(-3)xx9.8)/(2pi(4.25+4.35)xx10^(-2))` `=(3.97xx9.8)/(2pixx8.6)xx10^(-1)=0.07199N//m`