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NEET-XI-Physics

exam-2 year:2016

with Solutions - page 3
Qstn# 126 Prvs-QstnNext-Qstn
  • #126
    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:-
    (1)``\frac{\pi}{2} < `` ``\theta_1`` < ``\theta_2`` < ``\theta_3`` <``\pi``
    (2)``\pi`` > `` ``\theta_1`` > ``\theta_2`` > ``\theta_3`` ``\frac{\pi}{2}``
    (3)``\frac{\pi}{2}`` > ``\theta_1`` > ``\theta_2`` > ``\theta_3`` ``\geq 0 ``
    (4)0 `` \leq `` ``\theta_1`` < ``\theta_2`` < ``\theta_3`` ``\frac{\pi}{2}``
    digAnsr:   4
    Ans : (4)
    Sol. h =
    2Tcos
    gr


    As r, h, T are same,
    cos
    constant

    =

    &implies;
    1 2 3
    1 2 3
    cos cos cos  
    = =
      
    As 1 >2 >3
    &implies; cos 1 > cos 2 > cos 3 &implies;1 <2 <3
    As water rises so must be acute
    So, 0 1 < 2 < 3 < /2