How does the speed of light in a medium compare to the speed in a vacuum? a. It's the same, since the speed of light is a constant. b. The speed in the medium is always faster than the speed in a vacuum. c. The speed in the medium is always slower than the speed in a vacuum. d. The speed in the medium may be faster or slower, depending on the medium.

The speed of light, often denoted by the symbol \( c \), is an incredibly important constant in physics. In a vacuum, light travels at a speed of approximately 299,792,458 meters per second. This speed is considered the ultimate speed limit in the universe, meaning that nothing can travel faster than light in a vacuum.

Light speed is not just a number; it's a fundamental property that influences many aspects of physics. Albert Einstein's theory of relativity, for example, relies heavily on this constant.

When people talk about light speed, they're usually referring to light traveling in a vacuum, where there are no particles or materials to slow it down. In other words, the speed of light in a vacuum is the fastest that light can travel.

A vacuum is a space entirely devoid of matter. This means there are no particles, such as air molecules, that can interact with light.

Because there are no particles to get in the way, light can travel at its maximum speed in a vacuum, which is \( c \).

Understanding what a vacuum is helps explain why light travels faster in a vacuum than in other mediums. In everyday life, a perfect vacuum is hard to achieve, but outer space approximates this condition closely enough to be considered a vacuum for most practical purposes.

So, when light moves through a vacuum, there are no obstacles to slow it down, allowing it to travel at its fastest possible speed.

When light travels through a medium, such as water, glass, or even air, it interacts with the particles in that medium. These interactions cause the light to slow down compared to its speed in a vacuum.

This phenomenon occurs because light photons are absorbed and re-emitted by the particles in the medium, taking slightly longer paths as they move forward. The more dense the medium, the slower the light will travel through it.

For example:

• Light in water travels at about 75% of its speed in a vacuum.
• Light in glass travels at around 66% of its speed in a vacuum.

This slowing down is why things look bent or distorted when viewed through water or glass.

Therefore, as per the original exercise, option c ('The speed in the medium is always slower than the speed in a vacuum') is indeed correct.