Light travels slower through transparent objects than it does through a vacuum. The speed of light in a transparent object is determined by the refractive index of that material.

Here's why:

* Light interacts with matter: When light enters a transparent material, it interacts with the atoms and molecules within. This interaction causes the light to slow down.

* Refractive index: The refractive index is a measure of how much light slows down when it passes from a vacuum into a particular material.

* Formula: The speed of light in a material is calculated by dividing the speed of light in a vacuum (approximately 299,792,458 meters per second) by the refractive index of the material.

Example:

* The refractive index of water is approximately 1.33.

* The speed of light in water is approximately 225,000,000 meters per second (299,792,458 / 1.33).

Important points:

* Different materials, different speeds: The speed of light varies depending on the material. For example, light travels slower in glass than it does in water.

* Transparent vs. opaque: Light does not travel through opaque materials (like wood or metal).

* Refraction: The change in speed of light as it passes from one medium to another causes the light to bend, a phenomenon called refraction. This is why a straw appears to bend when placed in a glass of water.

Let me know if you'd like more details about refractive index or refraction!