Question

Two parallel wires each of length $10cm$ are $0.5cm$ apart. A film of water is formed between them. If the surface tension of water is $0.072N/m$, then the work done in on increasing the distance between the wires by $1mm$ is

• A. $1.44\times {10}^{-5}J$
• B. $1.72\times {10}^{-5}J$
• C. $1.44\times {10}^{-4}J$
• D. $1.72\times {10}^{-4}J$

Answer 1

The correct option is A $1.44\times {10}^{-5}J$

Work done (W) = increase in surface energy
$\Rightarrow W=2T\Delta A\because$ there are two free surfaces
$\Rightarrow W=2\times 0.072\times (10\times {10}^{-2}\times 1\times {10}^{-3})$$\Rightarrow W=1.44\times {10}^{-5}J$