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Thin liquid layer between two glass plates: force to separate them or surface tension

This type of question, asked 3 times: 20 Apr 2025 S1, 21 Apr 2025 S1, 14 May 2026 S1. All 3 questions below, oldest first.

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  1. Question 1

    20 Apr 2025 S1

    42
    A water drop of 0.01 cm30.01\,\text{cm}^3 is squeezed between two glass plates and spreads into an area of 10 cm210\,\text{cm}^2. If surface tension of water is 70 dyne/cm, then the normal force required to separate the glass plates from each other will be

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  2. Question 2

    21 Apr 2025 S1

    19
    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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  3. Question 3

    14 May 2026 S1

    109
    A drop of some liquid of volume 0.04 cm30.04\ \mathrm{cm^3} is placed on the surface of the glass plate. Then another glass plate is placed on it such that the liquid forms a thin layer of area 20 cm220\ \mathrm{cm^2} between the surfaces. To separate the plates a force of 16×10516 \times 10^5 dyne has to be applied normal to the surfaces. The surface tension of the liquid in dyne/cm is

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