Question

A film of soap solution is trapped between a vertical frame and a light wire $ab$ of length $0.1m$. If acceleration due to gravity $g=10m{s}^{-2}$ and surface tension $T=25\times {10}^{-3}N{m}^{-1}$, then the load $W$ that should be suspended from the wire to keep it in equilibrium is

• A. $0.2g$
• B. $0.3g$
• C. $0.4g$
• D. $0.5g$

Answer 1

The correct option is D $0.5g$

In the given condition, weight of the load is balanced by surface tension force i.e
$W=2Tl$ ($\because$ there are two surfaces of soap solution)
$\Rightarrow 2Tl=m\times g$

$25\times {10}^{-3}\times 2\times 0.1=m\times 10$

$m=\frac{5\times {10}^{-3}}{10}kg=0.5g$