A film of ethanol at 20^∘ C has a surface tension of 22.3 mN / m and is maintained on a wire fra

step 1 Here, assume a pre -surface on both side of the frame. There are two surfaces which is 20 multip

A film of ethanol at 20^∘ C has a surface tension of 22.3 mN...

A film of ethanol at $20^{\circ} \mathrm{C}$ has a surface tension of $22.3 \mathrm{mN} / \mathrm{m}$ and is maintained on a wire frame as shown in Fig. P4.73. Consider the film with two surfaces as a control mass and find the work done when the wire is moved $10 \mathrm{mm}$ to make the film $20 \times 40 \mathrm{mm}$

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Key Concepts

Surface Energy

Surface energy is the energy associated with the creation of a new surface area in a liquid. It is directly related to surface tension since the work required to create additional surface area is proportional to the product of the surface tension and the change in area.

Work Done Due to Change in Surface Area

In systems involving liquid films, the work done when the area of the film changes is computed by multiplying the surface tension by the change in surface area. This concept is key in calculating the energy input or output as the film is stretched or contracted.

Surface Tension

Surface tension is the property of a liquid surface that causes it to behave like a stretched elastic membrane. It is quantified as a force per unit length and represents the tendency of the liquid molecules at the surface to stick together, which minimizes the surface area.

Control Mass Approach in Surface Phenomena

Considering a control mass in problems involving surface tension means analyzing a defined mass of the film with fixed boundaries (in this case, the film with two surfaces). This approach helps in applying energy conservation principles to assess the work done on or by the system during its deformation.

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