Sunlight is slowed MOST when traveling through A) water. B) a vacuum. C) the atmosphere. D) None of these, as light always travels at the same speed.
The correct answer and explanation is:
Correct Answer: A) water
Explanation (300 words):
Light, or electromagnetic radiation, travels at different speeds depending on the medium it moves through. In a vacuum, such as outer space, light travels at its maximum speed: approximately 299,792 kilometers per second (km/s). This is the universal speed limit for light, often denoted as c in physics.
When light enters any material medium—such as air (the atmosphere), water, or glass—it interacts with the atoms and molecules in that medium. These interactions cause light to slow down. The amount of slowing is determined by the optical density of the medium, which is quantified using the refractive index (n). A higher refractive index means that light travels more slowly in that medium.
- Vacuum: Refractive index = 1.0
- Air (atmosphere): Refractive index ≈ 1.0003 (very close to a vacuum)
- Water: Refractive index ≈ 1.33
Because water has a significantly higher refractive index than both air and vacuum, light travels slowest in water. The refractive index of a material is calculated by the ratio:
n = c / v,
where v is the speed of light in the medium.
This slowing down doesn’t mean the light loses energy; rather, its wavelength shortens, though its frequency remains constant.
Option D is incorrect because light does not always travel at the same speed—it only travels at “c” in a vacuum. The speed changes when it enters other media.
Conclusion:
Sunlight slows down the most when traveling through water due to its higher refractive index compared to air or a vacuum. Thus, A) water is the correct choice.