Question

A wire forming a loop is dipped into soap solution and taken out so that a film of soap solution is formed. A loop of 6.28 cm long thread is gently put on the film is pricked with a needle inside the loop. The thread loop takes the shape of a circle. Find the tension in the thread. Surface tension of soap solution = $0.030N{m}^{-1}$.

Answer 1

$F_s=2Tsind\theta$

$2Rd\theta S=2Td\theta$

$T=RS$

now, R=?

$2\pi R=L$

$R=\frac{L}{2\pi }=\frac{(6.28\times {10}^{-2})}{2\times 3.14}={10}^{-2}$

$T={10}^{-2}\times 0.030$

$T=3.0\times {10}^{-4}N$