1
Two liquids A and B have A and B as contact angles in a capillary tube. If K = A / B, then identify the correct statement:
- K is negative, then liquid A and liquid B have convex meniscus.
- K is negative, then liquid A and liquid B have concave meniscus.
- K is zero, then liquid A has convex meniscus and liquid B has concave meniscus.
- K is negative, then liquid A has concave meniscus and liquid B has convex meniscus.
Answer
(4) K is negative, then liquid A has concave meniscus and liquid B has convex meniscus.
Solution
As per NCERT, an acute angle of contact ( < 90 , > 0) gives a concave meniscus (e.g. water–glass), and an obtuse angle of contact ( > 90 , < 0) gives a convex meniscus (e.g. mercury–glass).
K = A B < 0 A and B have opposite signs
one liquid has a concave meniscus and the other a convex meniscus. Option (4) (A concave, B convex) fits this.
(1), (2): both menisci of the same type A and B have the same sign K > 0, not negative.
(3): K = 0 A = 0 A = 90 , so liquid A has a flat (plane) meniscus, not convex.
Answer: (4)
JEE Main 2025 (Online) 4th April Morning Shift