First slide

Surface tension and surface energy

Question

If water rises in a capillary tube upto 3 cm. What is the diameter of capillary tube (Surface tension of water = 7.2 ×10^–2 N/m)

Moderate

A

9.6×10^–4 m
B

9.6×10^–3 m
C

9.6×10^–2 m
D

9.6×10^–1 m

Solution

$\begin{array}{l} h = \frac{2 Tcos θ}{rdg}, for water θ = 0^{\circ} \\ \Rightarrow r = \frac{2 T}{hdg} = \frac{2 \times 7 .2 \times 10^{- 2}}{3 \times 10^{- 2} \times 10^{3} \times 10} = 4 .8 \times 10^{- 4} \\ ∴ d = 2 r = 9 .6 \times 10^{- 4} m \end{array}$

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