Question

In to a vessel containing pure water a clean glass tube of radius \(3.6 \times 10^{-4}\,\text{m}\) is held vertically with \(12\,\text{cm}\) of the tube above the water level. Now the capillary tube is moved down in to the water so that only \(2\,\text{cm}\) of its length is above the water surface. Angle of contact \(\Theta\) at this position is (given surface tension of water \(= 7.2 \times 10^{-2}\,\text{N m}^{-1}\) and \(g = 10\,\text{m s}^{-2}\))

• A. \(\Theta = 45^\circ\)
• B. \(\Theta = 30^\circ\)
• C. \(\Theta = 15^\circ\)
• D. \(\Theta = 60^\circ\)

Hint:

When the available tube length above water is less than natural capillary rise, use \(h = h_0\cos\Theta\) to find the changed angle of contact.

Answer 1

The Correct Option is D