Question
Question: A wire forming a loop is dipped into soap solution and taken out so that a film of soap solution and...
A wire forming a loop is dipped into soap solution and taken out so that a film of soap solution and taken out so that a film of soap solution is formed. A thread of length 6.28 cm is gently put on the film and film is pricked with a needle inside the loop. Find the tension in the thread if surface tension of soap solution is 0.03 Nm-1.
A
18.84 × 10-4N
B
6 × 10-14N
C
3 × 10-4 N
D
9.42 × 10-4N
Answer
3 × 10-4 N
Explanation
Solution
2T sin θ = S 2r θ where S is surface tension and 2 rθ is length of thread AB.
Since θ is small ⇒ sin θ = θ
2T θ = S 2rθ
or T = Sr = .03 × 102 = 3 × 10-4N