Question

Which of the following statements is correct regarding the angle of contact θ_c of a liquid drop with a flat solid surface?

विकल्प

• On the increasing temperature, θ_c decreases.

• On adding impurities, θ_c remains the same.

• On adding a waterproofing agent, θ_c decreases.

• θ_c does not depend on the surface tension of a liquid (T).

Answer 1

On the increasing temperature, θ_c decreases.

Explanation:

• Effect of temperature on θ_c:
  On the increasing temperature, surface tension decreases, thus cosθ_c increases (∵ cosθ ∝ 1/T) and θ_c decreases, so on Increasing temperature θ_c decreases.
• Effect of impurities on θ_c:
  Solute impurities raise surface tension, causing θ_c to fall and the angle of contact θ_c to rise.
• The effect of waterproofing agent:
  Because of the waterproofing ingredient, θ_c rises. It changes from an acute to an obtuse angle.