The figure shows a soap film in which a closed elastic thread is lying. The film inside the thread is pricked. Now the sliding wire is moved out so that the surface area increases. The radius of the circle formed by elastic thread will
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When the soap film inside the elastic thread is pricked, the remaining film outside will contract to minimize its surface area due to surface tension. The elastic thread, being closed and flexible, will be pulled into a shape that minimizes the perimeter for a given area—a circle. As the sliding wire is moved out, increasing the area, the radius of the circular thread must increase to enclose the larger area, since for a circle, area A = . Therefore, the radius increases.
Final answer: increase