What is a key factor in determining how light behaves at the boundary of two different mediums?

The behavior of light at the boundary of two different mediums is significantly influenced by the arrangement of atoms in those mediums. This arrangement determines the optical properties of a material, including its refractive index, which affects how light travels through it. The refractive index measures how much light slows down in a medium compared to its speed in a vacuum. When light encounters a boundary between two different mediums, changes in speed can cause phenomena such as reflection, refraction, or transmission depending on the atomic structure and bonding within each medium.

In contrast, factors such as the size of the containers holding the mediums, the color of the lights, and the temperature of the mediums do not inherently affect how light behaves at the boundary in a fundamental way. These aspects may influence the experiment or observation but do not determine the fundamental optical properties that govern light's interaction with different materials.