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.2Tsin⁡θ=σΔl2Tθ=σ(2θ×r)T=σr=σ×2πr2π=0.030×6.28×10−22π N =3×10−4 N