JEE Advanced 2018 · Paper 1 · Physics Q3

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PhysicsMultiple correct+4 / -2Question 3 of 54

A uniform capillary tube of inner radius $r$ is dipped vertically into a beaker filled with water. The water rises to a height $h$ in the capillary tube above the water surface in the beaker. The surface tension of water is $\sigma$ . The angle of contact between water and the wall of the capillary tube is $\theta$ . Ignore the mass of water in the meniscus. Which of the following statements is (are) true?

For a given material of the capillary tube,

h

decreases with increase in

r

For a given material of the capillary tube,

h

is independent of

\sigma

If this experiment is performed in a lift going up with a constant acceleration, then

h

decreases

h

is proportional to contact angle

\theta

Answer and worked solution

Official answer: A, C

Jurin's law.
$h=\frac{2\sigma\cos\theta}{\rho gr}.$

(A) $h\propto1/r$ . True.
(B) $h\propto\sigma$ . False.
(C) In a lift accelerating upwards, $g_{eff}=g+a>g$ , so $h$ decreases. True.
(D) $h$ is proportional to $\cos\theta$ , not $\theta$ . False.

(A), (C)

Topics:Capillarity Surface tension Pseudo forces and non-inertial frames

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JEE Advanced 2018 · Paper 1, Physics question 3