In which of the following circumstances would electromagnetic waves travel
the fastest?
A. Through water
B. Through outer space
C. Through transparent glass
D. Through air at room temperature
The Correct Answer and Explanation is :
The correct answer is B. Through outer space.
Electromagnetic waves, such as light, travel at different speeds depending on the medium through which they are propagating. In a vacuum, such as outer space, electromagnetic waves travel at their maximum speed, which is approximately (3 \times 10^8) meters per second (the speed of light, denoted as (c)). This is the fastest speed at which information or matter can travel in the universe, according to Einstein’s theory of relativity.
When electromagnetic waves pass through a medium like air, water, or glass, their speed decreases due to interactions with the particles in that medium. The speed of light in air is slightly less than in a vacuum (around (99.97\%) of (c)), as air has a lower refractive index than water and glass. In water, the speed of light decreases further to about (75\%) of (c), while in glass, it slows down even more, to around (67\%) of (c) depending on the type of glass.
The reason for this reduction in speed is due to the refractive index of the medium. The refractive index (n) is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium. For example, the refractive index of air is about 1.0003, water is about 1.33, and typical glass can range from 1.5 to 1.9. The higher the refractive index, the slower the light travels through that medium.
In summary, electromagnetic waves travel fastest through a vacuum (outer space) because they are not impeded by any matter, while their speed decreases significantly when they traverse materials like water, glass, or air.