COMEDK · Physics · 11. Mechanical Properties of Fluids

A thread is tied slightly loose to a wire frame as shown 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

A becomes concave towards \(A\)
B becomes convex towards \(5 A\)
C Either (a) or (b) depending on the size of \(A\) with respect to \(B\)
D remains in the initial position

Verified Solution

Answer & Solution

Correct Answer

(A) becomes concave towards \(A\)

Step-by-step Solution

Detailed explanation

When portion \(A\) is punctured, the soap solution comes out of the hole. So, due to surface tension, the solution in part \(B\) tries to pull it toward itself. Thus, the thread becomes concave towards \(A\).

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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