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Model Paper 3 — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsModel Paper 33 Marks
Question
Mercury has an angle of contact equal to $140^{\circ}$ with soda-lime glass. A narrow tube of radius 1.00 mm made of this glass is dipped in a trough containing mercury. By what amount does the mercury dip down in the tube relative to the liquid surface outside? Surface tension of mercury at the temperature of the experiment is 0.465 N $m ^{-1}$. Density of mercury $=13.6 \times 10^3 kgm ^{-3}$. .
✓

Answer

Angle of contact between mercury and soda lime glass, $\theta=140^{\circ}$
Radius of the narrow tube, $r =1 mm=1 \times 10^{-3} m$
Surface tension of mercury at the given temperature, $s =0.465 N m ^{-1}$
Density of mercury, $\rho=13.6 \times 10^3 \frac{kg}{ m ^2}$
Dip in the height of mercury $= h$
Acceleration due to gravity, $g =9.8 \frac{m}{ s ^2}$
Surface tension is related with the angle of contact and the dip in the height as:
$
\begin{aligned}
& s=\frac{h \rho g r}{2 \cos \theta} \\
& \therefore h=\frac{2 s \cos \theta}{\operatorname{rog}} \\
& =\frac{2 \times 0.465 \times \cos 140}{1 \times 10^{-3} \times 13.6 \times 10^3 \times 9.8} \\
& =-0.00534 m \\
& =-5.31 mm
\end{aligned}
$
Here, the negative sign shows the decreasing level of mercury. Hence, the mercury level dips by 5.34 mm .

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