JEE Main & Advanced JEE Main Paper (Held on 10-4-2019 Morning)

  • question_answer The radtio of surface tensions of mercury and water is given to be 7.5 while the ratio of their densities is 13.6. Their contact angles, with glass, are close to\[135{}^\circ \]and\[0{}^\circ ,\]respectively. It is observed that mercury gets depressed by an amount h in a capillary tube of radius \[{{r}_{1}},\] while water rises by the same amount h in a capillary tube of radius \[{{r}_{2}}.\]The ratio, \[({{r}_{1}}/{{r}_{2}}),\]is then close to: [JEE Main 10-4-2019 Morning]

    A) 2/3                              

    B) 3/5

    C) 2/5      

    D) 4/5

    Correct Answer: C

    Solution :

    \[h=\frac{2{{S}_{1}}\cos {{\theta }_{1}}}{{{r}_{1}}{{\rho }_{1}}g}\]           \[h=\frac{2{{S}_{2}}\cos {{\theta }_{2}}}{{{r}_{2}}{{\rho }_{2}}g}\]           \[\Rightarrow \frac{{{r}_{1}}}{{{r}_{2}}}=\frac{2}{5}\]                 


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