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A thin liquid film formed between a U-shaped wire and a light slider supports a weight of $1.5 \times 10^{-2} \mathrm{~N}$ (see figure). The length of the slider is $30 \mathrm{~cm}$ and its weight negligible. The surface tension of the liquid film is
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The correct answer is:
$0.025 \mathrm{~Nm}^{-1}$
$0.025 \mathrm{~Nm}^{-1}$
The force of surface tension acting on the slider balances the force due to the weight.
$\begin{array}{ll}
\Rightarrow & \mathrm{F}=2 \mathrm{~T} \ell=\mathrm{w} \\
\Rightarrow & 2 \mathrm{~T}(0.3)=1.5 \times 10^{-2} \\
\Rightarrow & \mathrm{T}=2.5 \times 10^{-2} \mathrm{~N} / \mathrm{m}
\end{array}$
$\begin{array}{ll}
\Rightarrow & \mathrm{F}=2 \mathrm{~T} \ell=\mathrm{w} \\
\Rightarrow & 2 \mathrm{~T}(0.3)=1.5 \times 10^{-2} \\
\Rightarrow & \mathrm{T}=2.5 \times 10^{-2} \mathrm{~N} / \mathrm{m}
\end{array}$
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