fellow students with slots in here and today we're going to look at how to draw re diagrams of converging lenses this picture here it just shows the sort of diagram that we'll be drawing so we have a couple learning goals today you should be able to draw ray diagrams for converging lenses and you should be able to describe images produced by converging lenses so just like what we saw with the concave mirrors they're a different set of rules depending on the location of the original object so we have five different locations that we talked about and we'll have different rules for for several groupings of these so one of the locations is beyond two F prime so that means further from the mirror than two F Prime at two F Prime between two F Prime and F Prime at F prime and between F Prime and the lens so those are the five locations that we'll talk about the first three so object beyond to F prime like in this picture here at to F prime or between F prime and to F Prime those three all have the exact same rules so we're gonna group them together and I'm just going to do one example that covers all three now if you have an example in your worksheet that covers a different one you'll still be using these exact same rules so what we'll be doing just like what you saw with the mirrors it's really hard for me to draw on the tablet to get correct angles and have nice straight lines so I'm going to be using an animation to show you what I would be drawing and you'll follow along in your notes the drawing the way that the animation shows so our first rule is that if we have an incident light ray that's parallel to the principal axis and we're going to draw our arrow head on there to show that it's moving towards the lens so parallel to the principal axis it will refract through the focus so it will go through us and again we put another Arrowhead on there to show that the light is moving in that direction through F so that's our first rule our second rule is that if we have a light ray that's moving through the optical center it will continue on in the exact same direction so it won't refract it'll just move through in a straight line so those are our two rules that we'll be using for these three situations now since we started drawing our light rays at the top of the balloon that means where the light rays cross which in this picture is between F and 2f where they cross will also be the top of the balloon because where the light ray started is the top so where they cross will also be the top so we can draw our picture like this now the string of the balloon went straight down to the principal axis which means the string of the balloon of our image will go straight to the principal axis now it's upside down this time but it will go straight to the principal axis it doesn't go straight down it moves towards the principal axis because the original objects have the string moving towards the principal axis so this is what our final image would look like now if we're describing it for the size it's smaller attitude is inverted because they're facing in different directions the location is between F and 2f and the type is real it's real because it's on the other side of the lens and because lenses are transparent light can actually move through the lens so if it ends up on the opposite side of the lens from the original object that is real if it was on the same side then that would be virtual because light doesn't bounce off of the lens and come back like it would with a mirror so that would be a virtual image if it's on the opposite side then it will be a real image so let's take a insert these characteristics vary depending on which of those three locations written at the top depending on which of those locations your object is that you'll have slightly different characteristics here these are the rules that I just explained I'm not going to read through them but if you like you can pause the video and write them down for your notes so let's take a look at the example when the object is at F so in this case our first rule will be that an incident light ray traveling parallel to the principal axis will refract through F so this is the same as the first rule that we saw last time and again drawing the arrowheads on there the second rule an incident parallel light ray traveling through the optical center will continue on in the same direction so again the same rule that we saw last time what's different about this situation than the last one is that if we look at our refracted rays they are parallel to each other which means they will never cross now we know where the top of the balloon will be based on where they cross but if they never cross that means there will never be an image so if we look at the characteristics the characteristics are that there is no image so we can't describe it anytime the original object is located at F Prime there will never be an image so this is always the case when it's at F Prime and here again are the care or sorry these are the descriptions of our light rays I'm not going to read through them but pause the video if you'd like to copy them into your notes and then finally let's see what happens when the object is between F Prime and the lens so our first light ray will be parallel to the principal axis and it will refract through F our seconds will move through the optical center and continue on in a straight line so again the same two rules that we saw last time the difference here is that if we look at our refracted rays they're actually traveling away from each other if they're traveling away from each other they won't cross on that side of the lens however if we backtrack those refracted rays to the original first side of the lens we'll see that they do cross so if they're traveling away from each other we need to back up those rays so this is how it would look the orange one traveling backwards to the original side of the lens and same with the red line there and now we can see that those two will cross on the other side of the lens and where they cross that's the tip of the balloon so we'll draw the balloon again with our original object the string went straight down to the principal axis so when our image the string will go straight down to the principal axis and we'll have an image that looks like this on the same side of the lens as the original object so if we're describing this it's larger it is upright because they're both facing the same direction it's beyond 2 F Prime and let's type is virtual because it's on the same side of the lens as the original object and here are those rules if you'd like to copy them down in your notebook so let's take another look at our learning goals you should be able to draw re diagrams for converging lenses and you should be able to describe images produced by converging lenses if you can do these things fantastic if not please rewatch the video and if you still have in trouble come ask me in class tomorrow all right that's all for now bye bye