Given below are two statements:
Statement I : If a capillary tube is immersed first in cold water and then in hot water, the height of capillary rise will be smaller in hot water.
Statement II : If a capillary tube is immersed first in cold water and then in hot water, the height of capillary rise will be smaller in cold water.
In the light of the above statements, choose the most appropriate from the options given below

Solution

Physics sir · 3 steps

Heating water lowers its surface tension, and surface tension is what pulls the column up the tube.

1. h = (2T cos θ)/(rρ g)

2. What depends on temperature. The same tube means r stays fixed, and θ ≈ 0 for clean glass and water. Only the surface tension T and the density ρ change when the water is heated.
3. Which change wins. From about 20°C to 80°C, the surface tension of water falls by about 14%, while its density falls by only about 3%. So T/ρ goes down, and with it the height h.
4. So. The water rises less in hot water than in cold water. Statement I is true and Statement II is false, which is option (c).

The idea to keep. In capillarity questions, temperature acts through surface tension. Hotter liquid has lower T, so the rise h ∝ T/ρ goes down, even though the density also falls a little.

Answer from the NTA final answer key. Solution by PrepWiser.