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COMEDK2019PhysicsMechanical Properties of Fluids

A thread is tied slightly loose to a wire frame as in figure and the frame is dipped into a soap solution and taken out. The frame is completely covered with the film. When the portion A is punctured with a pin, the thread

Options

  1. Abecomes concave towards A
  2. Bbecomes convex towards A
  3. Cremains in the initial position
  4. DEither (a) or (b) depending on the size of A w.r.t. B

Correct answer

A. becomes concave towards A

Step-by-step solution

The potential energy due to surface tension is given by the formula U=S A where, S is the surface tension and A is the area of film. Since after puncturing, the film will try to minimise its potential energy and hence the surface area. Thus, the thread will become concave towards A.

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