in today's video we're going to look at the refraction of light waves which is when waves change direction as they pass from one medium to another like from air into glass and in doing so we'll also cover ray diagrams and triangular prisms in order to understand refraction you need to know that waves travel at different speeds in different materials or mediums and that this happens because different mediums have different densities electromagnetic waves like light the higher the density of the material the slower the wave will travel through it so if a wave travels from a less dense medium over to a more dense medium like from air into glass it will slow down as it passes into the glass if the waves traveling perpendicular to the boundary between the two materials like it is in this image then it will just continue straight on however if it hits the boundary at an angle like in this case then it'll be refracted which means that its direction will change if it's passing into a more dense medium like it is here because glass is more dense than air then it will bend towards the normal which remember is this dashed line perpendicular to the surface so we can see that instead of carrying straight on in this direction it's actually bent upwards a little bit towards our normal the next thing we need to look at is how to draw proper ray diagrams for refraction let's imagine that we have a piece of glass with an incident or incoming light ray like this and we have to draw the full ray diagram for the transmission of the ray through the piece of glass the first step is to draw our normal which will be perpendicular to the glass surface at our point of incidence which is where the light ray hits the glass now we know that if the incident ray didn't change direction then it would look like this but because it's entering a more dense medium the wave will slow down and bend towards the normal so we're gonna have to draw it somewhere in this region in your exam it shouldn't matter exactly where you draw the new line so i suggest just drawing it about halfway towards the normal like we are here we call this line the refracted ray and we have to continue it all the way to the other side of the piece of glass at this point we just repeat the process so we draw our normal think about where the ray would be if it didn't change direction and then consider which way it's going to bend this time it's passing from the more dense glass to the less dense air so it will speed up and bend away from the normal so something like this and we call this ray the emergent ray to complete the diagram we also need to add the angle of incidence and the angle of refraction as well the last thing i want to mention is that because the speed of the wave is changing as it passes from one medium to another then by our wave speed equation which says that wave speed equals frequency times wavelength the frequency or the wavelength must be changing as well and you need to remember that the frequency always stays the same it's only the wavelength that changes so if the speed of a wave increases the wavelength must increase as well and vice versa interestingly though different wavelengths of lights are refracted by different amounts and this means that if we put white light which contains all the wavelengths of visible light through a triangular prism then the different colors will bend to different degrees and so they'll all spread out like a rainbow that's everything for this video though so hope you enjoyed it and we'll see you soon