There is a howizontal film of soap solution. On it a thread is placed in the form of a loop. The film is pierced inside the loop and the thread becomes a circular loop of radius `R`. If the surface tension of the loop be `T`, then what will be the tension in the thread?

Options

A. `pi R^(2)/T`
B. `pi^(2)R^(2)T`
C. `2piRT`
D. `2RT`

Answer

D

Explanation

Surface tension force is radially outwards.
On `AB`:
`2F sin theta=`surface tension force from two films from two sides
For small angle,
`sin d theta~~d thata`
`:. 2Fdtheta=2(Tl)=2(T)(2Rd theta)`
`:. F=2TR`.