A thin metal ring of internal radius 8 cm and external radius 9 cm is supported horizontally from the pan of a balance so that it comes in contact with water in a glass vessel. If is found that an extrea weight of `7.48g` is required to pull the ring out of water. The surface tension of water is `(g=10m//s^(2))`

Options

A. `80xx10^(-3)N//m`
B. `25xx10^(-3)N//m`
C. `45xx10^(-3)N//m`
D. `70xx10^(-3)N//m`

Answer

D

Explanation

`W=2pi (r_(1)+r_(2))T`
`:. T=(W)/(2 pi(r_(1)+r_(2)))=(7.48xx10xx10^(-3))/(2pixx17xx10^(-2))`
`=70xx10^(-3)N//m`.