Physics - Fluid Question with Solution | TestHub
Figure (a) and (b) show water drop and mercury drop in two identical conical glass pipes, then
Options:
Answer:
Solution:
Water wets glass, so its contact angle is acute. Mercury does not wet glass, so its contact angle is obtuse. The motion is caused by unequal curvature pressures at the two ends of a drop, not by the drop changing the material contact angle.
For water, the pressure inside a concave meniscus is lower than the outside pressure. The meniscus at the narrower end has stronger curvature and a larger pressure reduction. The resulting pressure difference drives water toward the narrow end.
For mercury, the convex meniscus produces a pressure increase. This increase is larger at the narrower end, so mercury is driven toward the wide end.
Therefore water moves toward the narrow end and mercury toward the wide end: option A. This uses the usual wetting and non-wetting assumptions for clean glass.
