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AMU Medical AMU Solved Paper-2004

  • question_answer
    Calculate the force required to separate the glass plate of area \[\text{1}{{0}^{-2}}\text{ }{{\text{m}}^{\text{2}}}\]with a film of  water 0.05 mm thick, [surface tension of water is \[\text{7}0\times \text{1}{{0}^{-3}}\text{ N}/\text{m}]\]

    A)  25 N                                     

    B)  20 N

    C)  14 N                                     

    D)  28 N

    Correct Answer: D

    Solution :

                     Surface tension (T) is defined as the force required to separate the surface area (A A) of liquid film by unity at constant temperature.                 \[T=\frac{W}{\Delta \,A}\]                                           ? (i) Since film of water consists of two films hence twice of surface area is taken. Also, W = force (.F) x displacement          ...(ii) From Eqs. (i) and (ii) and taking twice of surface area, we get                 \[F=\frac{2T\Delta A}{d}\] Given,   \[\Delta A={{10}^{-2}}{{m}^{2}}\],                 \[T=70\times {{10}^{-3}}N/m\],                 \[d=0.5\,mm=0.05\times {{10}^{-3}}m\] \[\therefore \]  \[F=\frac{2\times 70\times {{10}^{-3}}\times {{10}^{-2}}}{0.05\times {{10}^{-3}}}=28\,N\]


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