When a capillary tube is dipped in water, the mass of water lifted above the surrounding water level is 5 g. If a tube of double the radius is used instead, what mass of water will rise above the outside level?

10 g
5 g
1.25 g
20 g

Correct answer: 10 g

Solution

Capillary rise h = 2*S*cos(theta)/(rho*g*r), so h ~ 1/r. The mass raised m = rho*pi*r²*h ~ r²*(1/r) = r. Doubling r doubles the lifted mass: 5 g -> 10 g.

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