Question

A soap film of surface tension $3\times {10}^{-2}N{m}^{-1}$ formed in a rectangular frame, can support a straw. If the length of the film is 10 cm, then the mass of the straw that film can support is :

• A. 0.06 g
• B. 0.6 g
• C. 6 g
• D. 60 g

Answer 1

Answer: (B)

0.6 g

The weight of straw will be balanced by the force of surface tension.
Let the mass of straw is m, then
$mg=2Tl$ or $m=\frac{2Tl}{g}$
$=\frac{1\times 3\times {10}^{-2}\times 10\times {10}^{-2}}{9.8}kg$
$=0.6g$