Question

A soap film of surface tension $3 \times 10^{-2} Nm ^{-1}$ formed in a rectangular frame can support a straw as shown in figure. If $g=10$ $ms ^{-2},$ the mass of the straw is

• A. 0.006 g
• B. 0.06 g
• C. 0.6 g
• D. 6 g

Answer 1

Answer: (C)

As soap film can support the straw,
$m g=2 \sigma l$
$m=\frac{2 \sigma l}{g}=\frac{2 \times\left(3 \times 10^{-2} \frac{ N }{ m }\right) \times(0.1 m )}{10 \frac{ m }{ s ^{2}}} \frac{\uparrow^{2 \sigma l}}{\downarrow_{m g}^{ Start }}$
$=6 \times 10^{-4} kg =0.6$ gram.