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What is the Speed of Light?

Physics | 7-14 yrs | Reading Pod

Do you know what is the fastest thing ever?

The cheetah? From the animal kingdom? Sure!

Usain bolt? In humans, yep!

But do you know what is faster than the fastest? Look around you!
Any guesses?

It is… LIGHT!

How “Fast” is the Speed of Light?

Mathematically, light travels at the speed of 300000000 meters per second in vacuum. It is a constant quantity which remains the same throughout the reaches of humans.

This constant attribute, though changes when the medium changes. In vacuum, there is no obstacle for the light waves and hence, it travels unobstructed.

Let us now analyze the difference in the speed of light as the medium in which it travels changes:

Speed of light in,

  • Vacuum: 3 x100000000 meters per second.
  • Water: 2.26 x100000000 meters per second.
  • Air: 2.9 x100000000 meters per second.
  • Glass: 1.9 x100000000 meters per second.

As opposed to what is written above that the speed of light is constant throughout, why do we see such discrepancy in the speeds while traveling through different mediums then?

Light has a dual nature. It means light behaves as particle as well as waves. Hence, it has the properties of waves as well as particles. Due to this, when light travels through vacuum, it has no obstructions on the way. Where as when it travels through any medium, such as water, the atoms and molecules pose as a hindrance for light to travel at its constant speed, gets absorbed and re-emitted and hence, its speed lowers. Medium or no medium, speed of light still leads the charts for being the fastest!

How do we calculate the speed of light in different mediums?

The speed of light can be calculated according to the following formula:
Speed of light in vacuum/ refractive index of the medium

Note: The refractive index of a given medium is the amount of bending of light when it passes from one medium to another.

So what is the speed of light in diamond given the refractive index being 2.41?

Speed of Light Formula

Speed of light in diamond = Speed of light in vacuum/ refractive index of diamond
= 3 x100000000 / 2.41 (meters per second.)
= 1.2 x100000000 meters per second.

Fact about the Speed of Light

Up till now, traveling with the speed of light has not been possible. Hypothetically speaking, if we do travel with the speed of light we can circle the Equator 7.5 times in one second!

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