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Discussion Forum



1)

A uniform capillary tube of inner radius r is dipped vertically in to 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 the water is $\sigma$ . The angle of contact between water and the wall of the capillary tube is θ . Ignore the mass of water in the meniscus. Which of the following statements is (are)  true ?


A) For a given material of the capillary tube, h decreases with increase in r

B) For a given material of the capillary tube , h is independent of $\sigma$

C) If this experiment is performed in a lift going up with a constant acceleration, then h decreases

D) h is proportional to contact angle$\theta$

Answer:

Option (A,C)

Explanation:

$h=\frac{2\sigma\cos\theta}{r\rho g}$

$(a)   \rightarrow  h\alpha\frac{1}{r}$

 (b) h depends upon  $\sigma$

(c)   If lift is going up with  constant acceleration

    $g_{eff}= (g+a)\Rightarrow h= \frac{2\sigma \cos\theta}{r\rho (g+a)}$

    It means h decreases.

(d)  h is proportional $\cos\theta$