Chapter 12.3, Problem 24SSC

Interpretation Introduction

Interpretation:

The reason for surface of mercury in a thermometer to be convex must be explained.

Concept introduction:

Mercury doesn’t wet the glass. There is different forces within drops and between drops and glass.

Answer to Problem 24SSC

The cohesive forces within the drop[s of mercury is stronger than adhesive forces between the drops and glass. So the surface of mercury is convex in a thermometer.

Explanation of Solution

Between mercury atoms there is stronger cohesion force as compared to atom of mercury and glass. The stronger cohesion force between mercury atoms in the liquid mercury try to make it a drop. The contact angle ?c (angle between surface and wall of the glass) is greater than 90°.

Conclusion

Due to stronger cohesion force between mercury atoms than adhesion force between mercury and glass the surface of mercury is convex in a thermometer.