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Physics · PYQ NEET UG 2016(2)
हिन्दीThree liquids of densities \( \rho_1, \rho_2 \) and \( \rho_3 \) (with \( \rho_1 > \rho_2 > \rho_3 \)), having the same value of surface tension T, rise to the same height in three identical capillaries. The angles of contact \( \theta_1, \theta_2 \) and \( \theta_3 \) obey
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Correct answer · Option C
\( 0 \le \theta_1 < \theta_2 < \theta_3 < \frac{\pi}{2} \)
Explanation
Height of liquid rise in capillary is \( h = \frac{2T \cos\theta}{r \rho g} \). Since \( h, T, r, g \) are constant, \( \rho \cos\theta = \text{constant} \), so \( \cos\theta \propto \rho \). Since \( \rho_1 > \rho_2 > \rho_3 \), we have \( \cos\theta_1 > \cos\theta_2 > \cos\theta_3 \), which implies \( \theta_1 < \theta_2 < \theta_3 \).
