hello great T in this video we're going to be focusing on the introduction to transverse waves and in particular we'll be looking at transverse pulses and we'll be looking at the principle of superposition constructive interference and destructive interference let's go in the previous video our introduction video we briefly looked at the three different types of waves that we will be learning about this year now remember transverse waves or mechanical waves they need a medium to travel through they need air they need water so when you think of a transverse wave I want you to think of ocean waves I want you to think of you drop a stone in a pond and you see the ripples those ripples represent a transverse wave now what's very important to note about transverse waves is that transverse waves are made up of a series of pulses now what is a pulse a pulse is a single disturbance in a medium a single disturbance in in a medium okay so it's the effect of a single vibration we get an external Source such as me dropping a stone into a pond so a single vibration would be a pulse and a train or series of pulses makes up the wave so if you look at this diagram that I have over here we have this person and this person is shaking this rope so this over here would represent one pulse a series of those would would make up a wave pulses are made up of a little amplitude so we will go into amplitude in more detail when we do transverse waves but it's basically the distance from here to here that's the amplitude we've got a pulse width and obviously the pulse travels with a particular velocity or speed now a transverse pulse is called a transverse pulse because remember we said that transverse is all about how the particles move so transverse pulse is a pulse in which the particles of the medium like the air or the water move at right angles to the direction of motion of the pulse and in the previous video we said that's basically like the little particles are moving up and down but the pulse is moving left to right and you can see that on this diagram that I have over here particle oscillation oscillation just means movement the particles move up and down but the pulse will travel to the right can you see that if this moves up and down but the pulse is traveling to the right that's at right angles and that's why it's called a transverse pulse now when dealing with pulses we can have something called the principle of superposition superposition is the algebraic sum of the amplitudes of the two pulses that occupy the same space at the same time sounds fancy but basically all that this is saying is if I have a pulse like this going to the right and a pulse like this going to the left what happens when they occupy the same space at the same time because remember at the moment they're traveling towards each other at one point in time they are going to be overlapping one another so the principle of superposition is all about what happens when they at the same space at the same time time and here's an example of what would happen so say for example I have a pulse so this would represent one pulse pulse a and this would represent another pulse pulse B they are traveling towards each other pulse a is going to the right pulse B is going to the left this says before superposition remember superposition going back that is just going to be the algebraic sum of the amplitudes of two pulses that occupy the same space at the same time so basically superposition will occur when they occupy the same space at the same time so pulse a pulse B when they occupy the same space at the same time that's when superp position is going to happen look what happens because this is 2 cm making a little upwards hump over here of 2 cm and this one over here of 1 cm a 2 cm Crest we call this a Crest and a 1 cm Crest when they join it's going to be 3 cm why because it's the algebraic sum 2 + 1 gives me 3 but this is important what happens after superposition is they continue in the original directions of motion so I hope this makes sense if pulse B which is over here if pulse B was originally going that way right it's originally originally going to the left and pulse a is 2 cm was origin originally going to the right after they meet each other they will continue in their original directions so if you take a look at the diagram we see that pulse B was going to the left pulse B this is pulse B continues going to the left pulse a was going to the right look at the top it was going to the right pulse a continues going to the right and their original amplitudes stay intact Remains the Same when superposition happens we can have two different types of interferences that take place we can have constructive interference and destructive interference and I want you to listen to those words constructive interference constructive means to build something up so look at what it says it says constructive interference is the phenomenon where the crest of one pulse overlaps with the crest of another and then we produce a pulse of increased amplitude so say pulse a has an amplitude of 2 cm and pulse B has an amplitude of 2 cm can you see that this Crest and this Crest they match up they will produce a pulse of 4 cm constructive is to build up it creates a pulse of increased amplitude so take a look at this one behind me over here this is before interference okay so Crest plus Crest overlaps and it produces a pulse with a greater amplitude and then they pass by like normal then we get destructive interference and destructive means to tear things down to break things down so destructive interference is the Phenomenon with the crest of one pole so yeah we got a Crest by the way a Cris as if it goes up like that a trough you see that word it's called a trough is when it goes down like that so destructive is when the crest of one pulse I'm going to use a highlighter crest of one pulse overlaps with the trough here's the trough of another pulse and it results in a pulse of reduced amplitude so in this example let's pretend that this Crest was 2 cm upwards and this trough was 2 cm downwards what's going to happen if you have 2 cm up and 2 cm down what is two because this is going up and this is going down we minus them if they're going up and up so Crest plus Crest we add them so 2 and two would give me four if I've got two and two so one going up and one going down we minus them what's 2 - 2 in this case it's zero so in this case they completely eliminate each other but we may get a scenario like this one so this is the one behind me is the same as the previous slide as you can see they cancel each other out and this will only be the case if the crest over here is 2 cm the amplitude here is 2 cm and the amplitude here is 2 cm or 6 cm and 6 cm then it makes sense but we could get a scenario like this one take a look at the scenario let's do example one first so ignore example two make myself bigger over here if you look at example one we've got a amplitude here of four I know it says negative but if you were if you had to State the amplitude of this pulse over here for me you would say that it's 4 cm why do you think they're saying -4 they're saying -4 because it's a trough it's going down so we've got a four going down and a six going up basically overall we have a Crest with a pulse of 2 cm once superp position occurs okay remember super position position is when they occupy the same space at the same time now you could say ma'am I don't get it how did you get two remember six is going upwards and four is going downwards six is a Crest so let's write it as a positive four is a trough so let's write it as a negative what is 6 - 4 2 and because two is a positive we're going to draw it as a Crest and remember once they've passed each other they continue with the same original amplitudes let's look at example number two so for example number two I have a Crest with 3 cm because it's a Crest we're going to write it with a positive 3 then it means let's call that a pulse a then it meets with pulse B which has an amplitude of 7 cm but because it's a trough look a is a Crest that goes like that b is a trough because it's a trough we're going to say Min - 7 what is 3 - 7 I get -4 now remember the four means that when superposition occurs our resultant or our overall pulse what happens is we're going to have a pulse of 4 cm but downwards a trough hope that makes sense so let me draw another example here if I had to have 3 cm as a Crest going that way and 3 cm or let's say 2 cm as a Crest going that way because they both Crest they will add to make 5 cm but if they go in opposite direction so let's say 8 cm is a Crest and let's say 1 cm is a trough what'll happen because it's 8 this way and one this way we say 8 - one we get seven so when superposition occurs it'll be a pulse with an amplitude of 7 cm a little Crest and that is transverse pulses in the next video we will look at transverse waves I'll see you then