U-shaped wire is dipped in a soap solution,and removed.The thin film formed between the wire and the light slider,supports a weight of $1.5\times 10^{-2}N$(which includes the small weight of the slider).The length of slider is 30cm.What is the surface tension of the film?

Question

$\begin{array}{1 1}(A)\;2.5\times 10^{-2}N/m\\(B)\;3.5\times 10^{-2}N/m\\(C)\;3\times 10^{-2}N/m\\(D)\;2.5\times 10^{-3}N/m\end{array}$