First slide

Surface tension and surface energy

Question

When a long glass capillary tube of radius 0.015 cm is dipped in a liquid, the liquid rises to a height of 15 cm within it. If the contact angle between the liquid and glass to close to 0º, the surface tension of the liquid, in milliNewton $m^{- 1}$ , is $[ρ_{(l i q u i d)} = 900 k g m^{- 3}, g = 10 m s^{- 2}]$ (Give answer in closest integer)

Easy

Solution

$\begin{array}{l} Rise = h = \frac{2 Tcos θ}{r ρ g} \\ \Rightarrow 15 \times 10^{- 2} = \frac{2 \times T \times 1}{0.015 \times 10^{- 2} \times 900 \times 10} \\ \Rightarrow T = 101.25 mN / m \\ t h e v a l u e o f s u r f a c e t e n s i o n i s c l o s e s t t o 101.00 \end{array}$

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