Q 11-09-162JEE MainJEE Main 2025 (4 Apr, Shift 1)Easy
Two liquids A and B have $\theta_A$ and $\theta_B$ as contact angles in a capillary tube. If $K = \cos\theta_A/\cos\theta_B$, then identify the correct statement:
Answer: (C) K is negative, then liquid A has concave meniscus and liquid B has convex meniscus.
An acute contact angle ($\cos\theta > 0$) gives a concave meniscus; an obtuse one ($\cos\theta < 0$) gives a convex meniscus.
$K < 0$ means $\cos\theta_A$ and $\cos\theta_B$ have opposite signs, so one liquid has a concave and the other a convex meniscus. Options (1) and (2) are therefore wrong, and option (3) is the possible case.
$K = 0$ means $\theta_A = 90^\circ$, a flat meniscus for A, so (4) is wrong.
Solution by Sreeraj P, M.Sc Physics