Question:
A liquid drop of volume V is placed on the surface of glass plate. Then another glass plate is placed on it such that liquid forms a thin layer of area A between the surfaces of two plates. To separate the plates a force F has to be applied normal to the surfaces. The surface tension of the liquid is
A liquid drop of volume V is placed on the surface of glass plate. Then another glass plate is placed on it such that liquid forms a thin layer of area A between the surfaces of two plates. To separate the plates a force F has to be applied normal to the surfaces. The surface tension of the liquid is
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A thin liquid film of thickness V/A has two free surfaces; the force balances surface tension on both.
Updated On: Nov 13, 2026
- \(\frac{\mathrm{FV}}{2\text{ }\mathrm{A}}\)
- \(\frac{\mathrm{FV}}{2\text{ }\mathrm{A}^{2}}\)
- \(\frac{\mathrm{FV}}{\mathrm{A}^{2}}\)
- \(\frac{F}{VA}\)
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept
The film thickness is \(t=\dfrac{V}{A}\). The excess pressure inside the film is \(\dfrac{2T}{t}\) (two free surfaces), and this acts over area \(A\).
Step 2: Force balance
\(F=\dfrac{2T}{t}\times A=\dfrac{2TA}{V/A}=\dfrac{2TA^{2}}{V}\)
Step 3: Solve for T
\(T=\dfrac{FV}{2A^{2}}\), which is option (B).
Final Answer:
The surface tension is F V divided by 2 A squared. \[ \boxed{\text{(B) }\dfrac{FV}{2A^{2}}} \]
The film thickness is \(t=\dfrac{V}{A}\). The excess pressure inside the film is \(\dfrac{2T}{t}\) (two free surfaces), and this acts over area \(A\).
Step 2: Force balance
\(F=\dfrac{2T}{t}\times A=\dfrac{2TA}{V/A}=\dfrac{2TA^{2}}{V}\)
Step 3: Solve for T
\(T=\dfrac{FV}{2A^{2}}\), which is option (B).
Final Answer:
The surface tension is F V divided by 2 A squared. \[ \boxed{\text{(B) }\dfrac{FV}{2A^{2}}} \]
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