Capillary Tubes
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-124
2025-11-08
46
The tubes used in the preceding demonstrations - if very small - have received the name of capillary tubes, from the Latin word capillus, which means "hair." The attraction which causes liquids to go up into minute openings is sometimes called capillary attraction. It is really only adhesion and surface tension. The water rises a little at the sides of a glass tube, and surface tension first makes the surface concave upward, and then tends to decrease the area of the surface by flattening the curvature. This draws the water level up higher inside the tube, and the process. continues until the adhesion and surface tension are counterbalanced by the weight of the column of water above the general level.
Experiment has established the following laws:
- When a liquid wets the surface of a tube placed in it, the surface of the liquid will be concave, and the liquid will rise in the tube. When the liquid does not wet the tube, the surface of the liquid will be convex, and the liquid will be depressed in the tube.
- The elevation or the depression varies inversely as the diameter of the tube.
- The elevation or the depression decreases as the temperature rises
Demonstrations. - Draw from a piece of soft glass tubing a fine capillary tube. Break out a piece about a foot long, having a uniform diameter, and put one end in water. Moisten the inside of the tube by drawing it full of water and blowing it out again. Hold the tube vertically and measure the height of the water in it. Draw the tube gently from the water and notice whether there is any change in the length of the water column. Break the tube and, taking a piece an inch shorter than the length of the measured water column, put it in water as before.
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