First slide

Surface tension and surface energy

Question

The angle of contact between glass and water is 0^o and water (surface tension 70 dyne/cm) rises in a glass capillary up to 6 cm. Another liquid of surface tension 140 dyne/cm, angle of contact 60⁰ and relative density 2 will rise in the same capillary up to

Moderate

A

12 cm
B

3 cm
C

24 cm
D

6 cm

Solution

$R i s e i n c a p i l l a r y = h = \frac{2 T \cos θ}{ρ g r}$
$\begin{matrix} ∴ \frac{h_{2}}{h_{1}} = \frac{σ_{2} \cos θ_{2}}{ρ_{2}} \times \frac{ρ_{1}}{σ_{1} \cos θ_{1}} \\ ⇒ \frac{h_{2}}{h_{1}} = \frac{140 \times \frac{1}{2}}{2} \times \frac{1}{70 \times 1} \\ \Rightarrow h_{2} = \frac{h_{1}}{2} = \frac{6}{2} cm = 3 cm \end{matrix}$

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