SIMPLIFIED: "25.3: The Law of Refraction"

Article Link: https://phys.libretexts.org/Bookshelves/College_Physics/College_Physics_1e_(OpenStax)/25%3A_Geometric_Optics/25.03%3A_The_Law_of_Refraction 

Note: The image above was taken from the original article.

Light does not always travel in a straight line. For instance, light may bend when it hits water, or another medium. This bending due to light being in another medium is called refraction. A medium is essentially a change in matter that impacts the speed of the light. The speed of light in a vacuum is 3*10⁸ meters per second, but when light is inside of another medium, such as water like mentioned before, oil, or glass, the speed of light changes. The equation n= c/v can be used to figure out the index of refraction, which essentially just a number that measures the speed of light inside of that medium. “n” is always 1 if the medium is air, and the value of n changes as the medium changes. For instance, for water, the index of refraction (n) is approximately 1.33. The index of refraction will typically be given to you if you are solving problems, or a quick Google search will tell you what it is. It is typically not expected that these values are memorized. “n” represents the index of refraction, “c” is a constant of 3*10⁸ meters per second which represents the speed of light in a vacuum, and “v” represents the speed of light inside of the medium “n”. “c” will always be 3*10⁸, so if you know the index of refraction (n) or velocity of light inside of the index of refraction, then you can find the other through that equation.

Additionally, there is another equation related to refraction called “Snell’s Law”. This equation is also referred to as the law of refraction, and the equation is: n1sin1=n2sin2. This equation initially may look complicated, but in reality, it is very simple. Theta 1 refers to the angle of the incoming ray of light relative to the vertical, and n₁ refers to the index of refraction that the incoming ray of light is in. Theta 2 refers to the angle of the outcoming ray of light relative to the vertical in the second medium, while n₂ refers to the index of refraction of the second medium. An application of this equation being useful is this situation: you might know the angle of light coming from the air, and you want to figure out what the outgoing ray of light will be when it is in water. Since you know both indices of refraction of air and water, in addition to the angle of light coming from the air (which is theta 1), you will be able to solve for theta 2.

Ultimately, refraction is a key concept in geometric optics, which deals with light rays, lenses, and mirrors. Refraction is responsible for some of the light bending that happens in our world.