A ring of internal and external diameters `8.5 xx 10^(-2)m` and `8.7 xx 10^(-2)m` is supported horizontally from the pan of a physical balance such that it comes in contact with a liquid. An extra force of 40N is required to pull it away from the liquid . Determine the surface tension of the liquid?

Options

A. `72dyn//cm`
B. `70.80dyn//cm`
C. `63.35 dyn//cm`
D. `60 dyn//cm`

Answer

A

Explanation

`[2pixx8.7/2+2pi+8.5/2]sigma=3.97xx980`
or `sigma=(3.97xx980xx7)/(22xx17.2) dyn//cm^(1)=72dyn//cm^(1)`