TeXes Science Practice Test

How does light wave speed change when traveling from space into an air atmosphere?

1. It increases

2. It decreases

3. It remains constant

4. It becomes unpredictable

The correct answer is: It decreases

When light waves travel from a vacuum, such as space, into an atmosphere like air, they encounter a medium that has a different density than a vacuum. As light enters air, it slows down. This change in speed happens because light interacts with the atoms and molecules present in the air, causing it to be refracted. The speed of light in a vacuum is approximately 299,792 kilometers per second, but in air, it slows down slightly to about 99.97% of that speed due to the density of the air. The change in speed is a fundamental principle of physics and is described by Snell’s Law, which relates the angles of incidence and refraction to the refractive indices of the two media. In atmospheric conditions, while the discrepancy in speed is minor, it is crucial in understanding phenomena such as the bending of light and the formation of images in lenses. Thus, when light transitions from space to air, it experiences a decrease in speed due to the differences in density and refractive index between the two environments.