Final answer:
The idea that light changes speed and direction when passing from one medium to another is called refraction, which is explained by Snell's Law using the indices of refraction. Light also exhibits straight-line propagation, reflectivity, and can cast shadows when obstructed. These principles are foundational to geometric optics.
Step-by-step explanation:
Law of Refraction and Light Propagation:
When light travels from one medium to another, its speed changes, which results in a change in direction. This phenomenon is known as refraction. The relationship between the angle of incidence and the angle of refraction is described by Snell's Law, which considers the indices of refraction of the two media involved. If medium 2 has a higher index of refraction than medium 1, this implies that light will travel slower in medium 2 and will bend towards the perpendicular to the surface as it enters medium 2, analogous to a lawnmower moving from a footpath to grass. Conversely, if light moves from a medium with a higher index to a lower one, it will speed up and bend away from the perpendicular, similar to a lawnmower moving from the grass back onto a footpath. Refracted light can also be used to form images, and the behavior of light rays adheres to principles of independence and reversibility.
Additionally, light propagation is defined by straight-line movement through uniform media, known as straight-line propagation. It reflects off surfaces in line with the law of reflection, creating angles of incidence equal to angles of reflection. When an opaque object blocks light, it casts a shadow by obstructing the light rays. All these principles form the basis of geometric optics, helping us understand light interactions with materials and surfaces.