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NEET NEET SOLVED PAPER 2016 Phase-II

  • question_answer
    Three liquids of densities\[{{\rho }_{1}},{{\rho }_{2}}\]and\[{{\rho }_{3}}\](with \[{{\rho }_{1}}>{{\rho }_{2}}>{{\rho }_{3}})\], having the same value of surface tension T, rise to the same height in three identical capillaries. The angles of contact \[{{\theta }_{1}},{{\theta }_{2}}and\,{{\theta }_{3}}\] obey

    A)  \[\frac{\pi }{2}>{{\theta }_{1}}>{{\theta }_{2}}>{{\theta }_{3}}\ge 0\]

    B)  \[0\le {{\theta }_{1}}<{{\theta }_{2}}<{{\theta }_{3}}<\frac{\pi }{2}\]

    C)  \[\frac{\pi }{2}\le {{\theta }_{1}}<{{\theta }_{2}}<{{\theta }_{3}}<\pi \]

    D)  \[\pi >{{\theta }_{1}}>{{\theta }_{2}}>{{\theta }_{3}}>\frac{\pi }{2}\]

    Correct Answer: B

    Solution :

    \[h=\frac{2T\cos \theta }{rpg}\] \[\Rightarrow r\,\alpha \,\cos \theta \] (as T, h and r are constants) \[\rho \uparrow \Rightarrow \theta \downarrow \] \[{{\theta }_{1}}<{{\theta }_{2}}<{{\theta }_{3}}\] Its rise so \[0\le {{\theta }_{1}}<{{\theta }_{2}}<{{\theta }_{3}}<\frac{\pi }{2}\]


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