Q 11-09-027NEETJEE MainEasy
When a glass capillary is dipped in mercury, the mercury level in the tube
Answer: (A) falls below the outside level, because the contact angle is obtuse
Concept. $h = \dfrac{2T\cos\theta}{\rho gr}$; an obtuse contact angle makes $h$ negative.
Step 1. Mercury on glass. $\theta \approx 140°$, $\cos\theta < 0$: the level is depressed and the meniscus is convex.
Answer. Falls below the outside level, because the contact angle is obtuse (Option A).
Solution by Sreeraj P, M.Sc Physics