Question:
If two glass plates have water between them and are separated by very small distance (see figure), it is very difficult to pull them apart. It is because the water in between forms cylindrical surface on the side that gives rise to lower pressure in the water in comparison to atmosphere. If the radius of the cylindrical surface is R and surface tension of water is T then the pressure in water between the plates is lower by:
If two glass plates have water between them and are separated by very small distance (see figure), it is very difficult to pull them apart. It is because the water in between forms cylindrical surface on the side that gives rise to lower pressure in the water in comparison to atmosphere. If the radius of the cylindrical surface is R and surface tension of water is T then the pressure in water between the plates is lower by:
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A cylindrical (one-curvature) liquid surface has excess pressure T/R, unlike a spherical surface (2T/R).
Updated On: Nov 11, 2026
- \(\frac{T}{R}\)
- \(\frac{T}{4R}\)
- \(\frac{4T}{R}\)
- \(\frac{2T}{R}\)
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The Correct Option is A
Solution and Explanation
For a cylindrical surface only one principal radius of curvature (R) exists, so the pressure difference across the surface is \(\Delta P=\frac{T}{R}\) (compare \(\frac{2T}{R}\) for a spherical surface).
The meniscus is concave towards the air, so the pressure in the water is lower than atmospheric by \(\frac{T}{R}\).
Answer: (1) \(\frac{T}{R}\)
The meniscus is concave towards the air, so the pressure in the water is lower than atmospheric by \(\frac{T}{R}\).
Answer: (1) \(\frac{T}{R}\)
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