Question

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

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

Answer 1

Answer: (C)

$0.6g$

In this case, upward surface tension force will support the straw. i.e.
$\Rightarrow 2T\times l=mg\because \text{there are two surfaces in soap film}$

$\Rightarrow 2\times 3\times {10}^{-2}\times 10\times {10}^{-2}=m\times 10$

$\Rightarrow m=6\times {10}^{-4}kg=0.6g$