Two glass plates are separated by water. If surface tension of water is 75 dynes per cm and area of each plate wetted by water is 8 cm² and the distance between the plates is 0.12 mm, then the force applied to separate the two plates is
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Two glass plates are separated by water. If surface tension of water is 75 dynes per cm and area of each plate wetted by water is 8 cm² and the distance between the plates is 0.12 mm, then the force applied to separate the two plates is

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Infinity Learn · Accepted Answer

The shape of water layer between the two plates
is shown in the figure.
Thickness d of the film = 0.12 mm = 0.012 cm.
Radius R of cylindrical face $= \frac{d}{2}$
$\begin{array}{l} F = T (2 I) = P (I \times 2 R) \\ P = \frac{T}{R} \end{array}$
Pressure difference across the cylindrical surface $= \frac{T}{R} = \frac{2 T}{d}$
Area of each plate wetted by water = A.
Force F required to separate the two plates is given by
F = pressure difference X area $= \frac{2 T}{d} A = \frac{2 \times 75 \times 8}{0 .012} = 1 N$

Surface tension and surface energy

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Two glass plates are separated by water. If surface tension of water is 75 dynes per cm and area of each plate wetted by water is 8 cm² and the distance between the plates is 0.12 mm, then the force (in newton) applied to separate the two plates is

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Surface tension and surface energy

Remember concepts with our Masterclasses.

Two glass plates are separated by water. If surface tension of water is 75 dynes per cm and area of each plate wetted by water is 8 cm2 and the distance between the plates is 0.12 mm, then the force (in newton) applied to separate the two plates is

Ready to Test Your Skills?

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Two glass plates are separated by water. If surface tension of water is 75 dynes per cm and area of each plate wetted by water is 8 cm² and the distance between the plates is 0.12 mm, then the force (in newton) applied to separate the two plates is