Refraction and optics

In the previous post I talked about the human eye and how it uses refraction. Today we will go into more detail about refraction.

Refraction is light bending when it changes medium as it travels. This is what causes a pen to look like it's bending when you put it in water. Sometimes, light bends inwards and sometimes bends outwards depending on the speed of each medium. The fastest speed the light can go at is in vacuum which is a massive number, nearly 300,000 km/s, which means that light can go around the earth 7.5 times in second. Let's put it this way, if you were a photon you would never be late for school.

In other mediums light travels slower. Scientists use something called the "refraction index" to compare the speed of light in vacuum vs another medium

• n is the refraction index in a given medium
• c is the speed of light in vacuum
• v is the speed of light in that medium

This table has some sample refraction indexes for transparent mediums.

So, for example the index of refraction of fresh water is 1.3333, which means that light in vacuum is 33% faster than in water.

Another thing we can see is that the more density the medium has the slower the light goes. Light has more obstacles to go through in a denser medium. As you can see the refraction index of ice is lower than in water, because water is one of the few liquids that becomes less dense when it turns into a solid.

Index of refraction allows to predict how much the light will bend. This is called Snell's law. Sadly, I don't know the maths to understand the formula YET.