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Surface Tension The surface of a polar liquid, such as water, can be viewed as a series of dipoles strung together in the stable arrangement in which the dipole moment vectors are parallel to the surface and all point in the same direction. Suppose now that something presses inward on the surface, distorting the dipoles as shown in Fig. 21.42.
(a) Show that the two slanted dipoles exert a net upward force on the dipole between them, and hence oppose the downward external force.
(b) Show that the dipoles attract each other and hence resist being separated. The force between dipoles opposes penetration of the liquid s surface and is a simple model for surface tension (see Section 143 and Fig. 14.15).
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