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 size of A w.r.t B

Answer 1

The correct option is B becomes concave towards A

When we puntured the film in part A, the pressure becomes equal to atmospheric pressure. So, applying the equation , if,

P=atmospheric pressure

T= surface tension constanT

R=radius of the film

If we start from the side below B, we get,

P+4T/R-4T/R=P

we equated it with the atmospheric pressure as we have punchered it from the A so, the pressure of that part becomes equal to atmospheric pressure.

So , to make it equal to atmospheric pressure , we need to have the thread with the shape concave towards A.