A thin cylindrical metal rod is bent into a ring with a small gap as shown in figure. On heating the system,

When a material undergoes thermal expansion due to an increase in temperature, the distance between its molecules or atoms increases. This increase in distance leads to the expansion of the material in all directions, affecting its overall dimensions.

Each molecule or atom within the substance gains energy with the rise in temperature, causing them to vibrate more vigorously and thus creating greater space between neighboring particles. This increased intermolecular distance results in the expansion of the material, affecting its length, area, or volume depending on the specific nature of the expansion.

This expansion occurs uniformly, meaning it affects all points within the material, causing an overall increase in size. This uniform increase in distance between particles contributes to the material's expansion without causing deformation or irregularities in its structure.