A loop of 6.28 cm long thread is put gently on a soap film in a wire loop. The film is pricked with a needle inside the soap film enclosed by the thread. If the surface tension of soap solution is 0.030 N/m, then the tension in the thread is

When the soap film enclosed by the thread is pricked, the thread would take up a circular shape. Consider a small element of the thread. While horizontal components of tension get balanced, the vertical components get added up.

$\begin{array}{l}\text{ or }2T\sin \theta =\sigma \mathrm{\Delta }l\\ \text{ or }2T\theta =\sigma (2\theta \times r)\\ \text{ or }T=\sigma r=\sigma \times \frac{2\pi r}{2\pi }=0.030\times \frac{6.28\times {10}^{-2}}{2\pi }\mathrm{N}\\ =3\times {10}^{-4}\mathrm{N}\end{array}$