Answer :
The height of capillary rise will be smaller in the second case when thecapillary tube is immersed first in cold water and then in hot water. This is because the surface tension of water decreases with increasing temperature, leading to a weaker capillary action and reduced rise of the liquid in the capillary tube.
Capillary rise occurs due to the cohesive forces between water molecules and the adhesive forces between water molecules and the walls of the capillary tube. When the capillary tube is immersed in cold water initially, the surface tension of water is higher due to the lower temperature. This results in stronger cohesive and adhesive forces, allowing water to rise higher in the capillary tube.
However, when the capillary tube is then immersed in hot water, the increased temperature leads to a decrease in surface tension. As a result, the cohesive and adhesive forces weaken, reducing the ability of water to rise in the capillary tube. This phenomenon is observed as a smaller height of capillary rise in the second case compared to the first case.
The relationship between surface tension and temperature is governed by the principles of intermolecular forces. As temperature increases, the kinetic energy of water molecules also increases, disrupting the hydrogen bonding network responsible for surface tension. Therefore, the decrease in surface tension with increasing temperature ultimately affects the capillary rise in the capillary tube immersed in hot water.
