Question

There is a horizontal film of soap solution. On it a thread is placed in the form of a loop. The film is punctured inside the loop and the thread becomes a circular loop of radius R

. If the surface tension of the soap solution be T , then the tension in the thread will be
A.. πR²/T
B.. πR²T
C.. 2πRT
D.. 2RT

Answer 1

The correct answer is C. 2πRT.

The tension in the thread after the film is punctured becomes 2πRT due to the surface tension of the soap solution, which causes the thread to form a circle with the smallest possible perimeter for the enclosed area.

Step-by-step explanation:

The phenomenon of surface tension is related to cohesive forces between molecules, which tends to minimize the surface area of a liquid.

When a loop of thread is placed on the surface of a soap solution and the film inside the loop is punctured, the surface tension of the soap solution causes the thread to form a circle, which has the smallest possible perimeter for an enclosed area.

The tension in the thread can be calculated considering that it experiences a force due to surface tension on both sides of the thread.

In this case, the tension in the thread due to surface tension T will be 2πRT, since the force is exerted around the entire circumference of the circle, which is 2πR.

Therefore, the correct answer is C. 2πRT.