Question

When the angle of contact between a solid and a liquid is \( 90^\circ \), then

• A. Cohesive force \(>\) Adhesive force
• B. Cohesive force \(<\) Adhesive force
• C. Cohesive force \( = \) Adhesive force
• D. None of these

Hint:

Angle of contact of \( 90^\circ \) indicates that the cohesive and adhesive forces balance each other.

Answer 1

The Correct Option is C

The angle of contact \( \theta \) is determined by the relative strengths of cohesive and adhesive forces.
It is given by: \[ \cos \theta = \frac{F_{\text{adhesive}} - F_{\text{cohesive}}}{\gamma} \] When \( \theta = 90^\circ \), we get \( \cos \theta = 0 \Rightarrow F_{\text{adhesive}} = F_{\text{cohesive}} \).
Hence, the cohesive and adhesive forces are equal.