Figure (a) and (b) show water drop and mercury drop in two identical conical glass pipes, then

Engineering

Physics

Surface Tension and Surface Energy

Capillary and Pressure Difference due to Surface Tension

Question

Figure (a) and (b) show water drop and mercury drop in two identical conical glass pipes, then

The water drop tends to move towards narrow end and mercury drop towards wide end.

both tend to move towards wide end.

both tend to move towards narrow end.

The water drop tends to move towards wide end and mercury drop towards narrow end.

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This question involves capillary action and contact angle. Water wets glass (contact angle < 90°) while mercury does not (contact angle > 90°). The meniscus shape differs, creating a pressure difference.

In a conical tube, the capillary rise height $h = \frac{2 γ \cos θ}{ρ g r}$ depends on radius $r$ . For water (θ<90°, cosθ>0), a smaller radius at the narrow end causes a higher rise, pulling the drop towards it. For mercury (θ>90°, cosθ<0), a smaller radius causes a depression, pushing the drop towards the wider end.

Final answer: The water drop tends to move towards the narrow end and the mercury drop towards the wide end.