Speed of Light – The Beginners Guide

speed of light

Technological advancements in space travel, hyperbole cars, communications, satellite technologies, sciences and research, and even in defense and military programs are based on the assumption that the speed of light is the fastest matter can travel.

The assumption is that nothing except well, it can actually travel with the speed of light. As an object (particle) approaches it, it decomposes into energy shedding its mass. Hence, it acts as an ultimate limit to how fast an object can travel within the confines of the known physical laws.

Of course, there have been reports of discoveries of particles breaking this momentum; however, rigorous testing has to be done, and the same result replicated before it can be accepted.

So, that still leaves it as the frame of reference in scientific calculations, the underpinning constant in space explorations, and the anchor in technological developments.

In this article, we’ll explain what the speed of light really is, the nature of it, we’ll also compare the speed of light with the speed of sound, then finally look at some areas of its applications.


Speed of Light Explained

It’s simply how fast it moves in a vacuum – a vacuum is a space with nothing, no air, no matter, just space. It has a value of 299,792,458 meters per second which are approximately 3.0 * 108 m/s and is represented by the letter C.

According to the theory of relativity, it moves with a constant momentum regardless of how fast or slows the observer is moving. In orders words, the brightness maintains a constant pace no matter how fast you’re moving towards it or away from it.

Bear in mind that light here means Electromagnetic radiation, which is the combination of all wave spectrum like the radio waves (has long wavelengths), infrared rays, gamma rays, ultraviolet rays, x-rays, and cosmic waves (short wavelengths).

The visible glow is only a tiny portion of the EM spectrum, and it lies somewhere close to the middle of the EM range.

When traveling through a different medium, it has been observed to be less than the one in a vacuum.


Speed of light in different medium

As it moves from one medium to another medium of varying density, it gets slowed down; this slowing is as a result of the scattering of the particles by the molecules of the material.

To illustrate this let’s look at what happens when a beam of radiance travels from air to water. The beam bends as it enters the denser medium (in this case water); the change in the direction of the beam signifies a change which is always less than its momentum when moving in a vacuum.

Here’s a list of an approximate velocity in some common mediums:

  • Air – 300, 000 km/s
  • Ice – 229, 000 km/s
  • Water (liquid) – 226, 000 km/s
  • Vegetable oil – 204, 000 km/s
  • Glass – 197, 000 km/s
  • Ruby – 170, 000 km/s
  • Diamond – 124, 000 km/s

As you can see from the list above, it decreases as the density of the medium it is traveling increases; this observation leads us to a concept known as refractive index.


Speed of light and the Index of Refraction

As we have established earlier, light is slowed as it moves through different mediums. Whether it’s traveling through the air, through a transparent object, or through water, its momentum is always impacted.

Hence, we can say that it’s refracted when there’s a change in its momentum and direction as it moves through a different medium.

So, the ratio in the vacuum and its momentum in any medium is called the refractive index of that material, and it is always greater than one.

The mathematical equation is;

n = c / v


Where n is the refractive index; it’s always greater than 1.


C is the velocity of light in vacuum

V is the velocity of light in the medium


In simple terms, this equation is saying that the speed of light changes as it travels through different mediums. It’s also implying that is greatest as it moves to a vacuum.

With this equation, it’s easy to determine how fast or slow a beam of brightness can travel between different materials.


Speed of Light vs. Speed of Sound

Let’s take a look at another phenomenon in nature – Sound. How does the velocity of sound compare to the velocity of light? Also, let’s examine how the sound behaves when passing through different mediums.

First, the sound is a type of energy produced when an object vibrates. It needs mediums to propagate, light speedunlike light which does not require any medium to propagate. And they travel through those mediums by vibrating the molecules of the material.

For instance, when traveling through a solid medium, sound waves vibrate the molecules of the material which are tightly packed hence, forcing them to collide with each other.

Just like the speed of light which is affected when it travels through a different medium, the velocity of sound is also impacted. Whereas, the speed of light is impeded, as the density of the material increases. Sound moves faster through the medium, the higher its density.

To illustrate this, let’s look at how fast sound travels through different materials. In a dry clear air at zero degree Celsius, the velocity of sound is 331.2 m/s, it travels at 1484 m/s in water, 5120 m/s in Iron, and 12000 m/s in diamond. Hence, it’s obvious then, that sound travels faster through solid mediums than liquid or gas.

So, how does these two compare? Light travels faster than sound. Remember, during a particularly stormy day with a thunderstorm, you always get to see the flashes of lightning first, before the rumbling of thunder follows. That exactly explains what I’ve been trying to describe for you.


Wrapping it up

Let’s recap, as part of the electromagnetic spectrum, has a constant momentum in a vacuum, c which has been calculated to be 2.9 *108 m/s.  As it moves through different mediums, it is refracted causing its momentum to change. The ratio in the vacuum with its momentum in the medium is known as the refractive index. But, sounds travel faster through a denser medium than light.

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