[Music] refraction happens when light changes Direction when it travels between substances of different densities the difference in densities between the substances affects the amount of refraction that takes place light slows down when it passes into a denser substance like from tic glass the angle of refraction is smaller than the angle of incidence as the light bends towards the normal passing through a less dense substance means the light speeds up and the Rays Bend away from the normal I use the acronym fast to remember which one's which so I don't get confused when drawing it every transparent substance has a refractive index which is the amount that it slows the light down compared to the speed of light in a vacuum is calculated using the equation sin I over sin R where I is the angle of incidence and R is the angle of refraction take this example where the angle of incidence is 65° and the angle of refraction is 40° this gives us a refractive index of 1.41 and will bend the light towards the normal refractive indices are good when it comes to making lenses so you can have powerful lenses without looking like [Music] this thanks for watching make sure to hit the like button and subscribed if you enjoyed the video and want to see some more you can also follow me on Twitter @ doai if you want to