Question

Figure shows a light capillary tube immersed in water. The top end of the tube is connected to a rod via uniform rod. The other end has a mass 'm'. The system is in equilibrium. Take contact angle to be $0^\circ$. Find T.

Answer 1

mg

Answer 2

The upward force due to surface tension in a capillary tube is given by $F_s = 2 \pi r S \cos \theta$. With $\theta = 0^\circ$, $F_s = 2 \pi r S$. This force supports the mass 'm'. For equilibrium, $F_s = mg$. The tension 'T' is the force exerted by the rod, which balances the upward surface tension force. Thus, $T = F_s = mg$.