Water rises to a height h in capillary tube. If the length of capillary tube above the surface of water is made less than h, then
- water rises upto a point a little below the top and stays there.
- water does not rise at all.
- water rises upto the tip of capillary tube and then starts overflowing like a fountain.
- water rises upto the top of capillary tube and stays there without overflowing.
Answer
(4) water rises upto the top of capillary tube and stays there without overflowing.
Solution
Capillary rise: h = 2S r g = 2SR g, where R = r is the radius of the meniscus.
hR = 2S g = constant
When the tube length h' < h, water reaches the top and the meniscus becomes flatter (larger radius R') so that h'R' = hR.
Water rises up to the top and stays there; it does not overflow (an overflow would give a perpetual-motion machine).
Answer: (4)