Question

A thread is tied slightly loose to a wire frame as shown in the 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 convex towards $A$.
• B. becomes concave towards $A$.
• C. remains in the initial position.
• D. either (a) or (b) depending on the size of $A$ w.r.t. $B$.

Answer 1

The correct option is B becomes concave towards $A$.

We know that when the portion $A$ is punctured with a pin, then the film on the portion $B$ is contracted to occupy the minimum surface area due to surface tension. Therefore, thread becomes concave towards $A$.