Consider a U-shaped frame with a sliding wire of length `l` and mass 'm' on its arm. It is dipped in a soap solution, taken out and placed in vertical position as shown in figure. Choose minimum value of m so that does not descent (Surface tension of soap solution is S)

Options

A. `(2Sl)/(g)`
B. `(Sl)/(g)`
C. `(Sl)/(2g)`
D. `(Sl)/(4g)`

Answer

D

Explanation

For wire to be in equilibrium,
`mg = 2Sl rArr m = (2Sl)/(g)`
For mass less than `(2Sl)/(g)` it will move upward So amongst the options `(Sl)/(4g)` is the minimum mass.