1. Tardigrade
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  3. Physics
  4. A rectangular frame of 7 cm × 5 cm hangs vertically by an arm of a balance. When its edge is just dipped in soap solution in container, extra mass of 0.4 g must be placed in opposite arm to balance the pull of the film in order to just raise it. Determine surface tension of soap solution in dyne/cm.

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Q. A rectangular frame of $7\, cm \times 5\, cm$ hangs vertically by an arm of a balance. When its edge is just dipped in soap solution in container, extra mass of $0.4\, g$ must be placed in opposite arm to balance the pull of the film in order to just raise it. Determine surface tension of soap solution in dyne/cm.

Mechanical Properties of Fluids

Solution:

A soap film is formed between edge (length) of frame and soap solution in container.
$\therefore T =\frac{ mg }{2 l}=\frac{0.4 \times 980}{2 \times 7}$
$=28\, dyne / cm$