Two liquids A and B have $\theta_{\mathrm{A}}$ and $\theta_{\mathrm{B}}$ as contact angles in a capillary…

Two liquids A and B have $\theta_{\mathrm{A}}$ and $\theta_{\mathrm{B}}$ as contact angles in a capillary tube. If $K=\cos \theta_A / \cos \theta_B$. then identify the correct statement:
  1. $K$ is negative, then liquid $A$ and liquid $B$ have convex meniscus.
  2. $K$ is negative, then liquid $A$ and liquid $B$ have concave meniscus.
  3. K is negative, then liquid A has concave meniscus and liquid $B$ has convex meniscus
  4. K is zero, then liquid A has convex meniscus and liquid B has concave meniscus.

Solution

$\mathrm{k}=\frac{\cos \theta_{\mathrm{A}}}{\cos \theta_{\mathrm{B}}}$
It is negative when $\cos \theta_A \& \cos \theta_B$ are of opposite sign. so option (3)

Asked in: JEE Main 2025 (04 Apr Shift 1)

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