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When a capillary tube is dipped into a liquid, the liquid neither rises nor falls in the capillary.(a) The surface tension of the liquid must be zero.(b) The contact angle must be 90°.(c) The surface tension may be zero.(d) The contact angle may be 90°. |
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Answer» (c) The surface tension may be zero. Explanation: The rise in a capillary tube is given as, h = 2S.cosθ/rρg The capillary tube has a certain inner radius r. So r, ρ and g are not zero. For h to be zero either surface tension S may be zero or the contact angle θ = 90° so that cosθ = 0. But we can not conclude that S must be zero or θ must be 90°. Hence the option (c) and (d) are true. |
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