A glass rod of radius R is dipped into water, which completely wets the glass (contact angle zero). Water rises around the rod. In a gravity-free environment, what is the radius of curvature Rc of the free liquid surface?

Correct answer: R

Solution

When the glass is completely wetted, the contact angle is zero, so the meniscus meets the surface tangentially and forms a hemispherical surface whose radius of curvature equals the radius R of the rod. Hence Rc = R.

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