MCQ
Two vertical parallel plates are partially submerged in water. The distance between plate is equal to $d$. Water rises due to surface tension $T$, the width of plate is $l$, and contact angle of water with glass is $0^o$. Find the force of attraction between the plates.
  • A
    $\frac{{{T^2}l}}{{\rho g{d^2}}}$
  • $\frac{{2{T^2}l}}{{\rho g{d^2}}}$
  • C
    $\frac{{{T^2}l}}{{2\rho g{d^2}}}$
  • D
    $\frac{{{T^2}l}}{{4\rho g{d^2}}}$

Answer

Correct option: B.
$\frac{{2{T^2}l}}{{\rho g{d^2}}}$
b
$\mathrm{F}=\left(\mathrm{P}_{0}-\mathrm{P}_{\mathrm{average}}\right) .$ $lh$

$\mathrm{F}=\left[\frac{2 T}{d}-\frac{\rho g h}{2}\right] \ell h$

$h=\frac{2 T}{\rho g d}$ so $\mathrm{F}=\frac{2 T^{2} \ell}{\rho g d^{2}}$

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