Frequency - Sixty Symbols

okay so I'd like to talk to you about a symbol that means a lot to me means a lot in terms of the work that I do which is related to nanoscience and so one of the fundamental symbols or one of the fundamental quantities related to a we're visits it's wavelength lambda or its frequency nu so that's spelt and you it comes from the Greek and it's that the Greek symbol nu looks looks like that that again is another convention that these symbols have been used alphabet a gamma nu Epsilon its historical they've been introduced by various physicists along the way so the other symbol that is used is is actually F and that's in the more recent textbooks including our first-year physics textbook you'll see F use more more than you don't quite know the reason for that I quite light nu myself but FS only used a little more I think perhaps the best way so if I bring out the trusty guitar here so frequency when I plug this this string at string vibrates back and forth at a certain rate per second there are so many vibrations per second that sets the air molecules into motion and then they in turn very back and forth and they vibrate back and forth on ryojun so the key thing with frequency is that's a relatively low frequency that's a relatively high frequency and all you're doing there is changing the number of times per second that string moves up and down you can think of it all in terms of sound waves but you can also think of it in terms of light waves so what with with light like that we can see in this room or light coming from distant stars that is actually another wave but in this case what it is is a wave of the electromagnetic field okay so what you have is a basically a field that's vibrating back and forth and what's interesting is in this case that they're fast without field vibrates back and forth then the different you see a difference in color and this goes all the way not just in terms of the visible spectrum that we can see where you go from red to blue so red is a relatively low frequency blue is a much higher frequency but it also goes all the way down to infrared actually down to much lower frequencies all the way up to x-rays which are very very hard very high frequency lots of vibrations per second if we place it a guess in the context of radio waves where because people are interested I've heard of kilohertz and megahertz and when we're talking about I guess the key thing is there is the vibrations on the atomic scale we're talking about at least a million times more a million to a billion times greater level of frequencies so these things are flipping back and forth very very very many more times a second than your conventional radio wave the interesting thing is that the smaller you make it the larger the frequency becomes so if I can grab a ruler and it's a really useful one so let's if we let's do a really simple demo so we've got something which here is 25 centimeters long so if we vibrate that we see that it oscillates it wobbles back and forth at a few times every second something like that so that's its resonant frequency that's the frequency it likes to to vibrate at and then so if we make it a little bit shorter so you know so it's 15 centimeters you'll see that the resonant frequency has increased we make it a little bit shorter still now we're down to nine centimeters you can see that dies out a little bit quicker but you can see that the frequency is as much as is greater and if you imagine trying to make that really really really really really small so this was only a few a fraction of a millimeter you know a few tenths or a few hundreds of a millimeter then the frequency actually goes up to tens or maybe hundreds of kilohertz thousands of Hertz and then if you go those extra few steps those extra few orders of magnitude as we see for powers of 10 down to the range of the individual atoms and molecules then we're going into the terahertz regime where you've got a bit of sorry a million million Hertz 10 to the 12 10 to the power of 12 volts we have this picture of atoms and molecules being and electrons and small particles being like billiard balls when in fact or not really at the quantum level in the nanos in the Nano world what we have are basically matter waves so matter stops behaving like these billiard balls we have this picture up in our heads and actually spread out and they have a way of associated with them and what's remarkable is there is the fundamental physics of waves the same type of physics that you apply to the guitar to a large extent you can also apply to the behavior of matter at the quantum level up until the early years of the 20th century the classical picture was that atoms is just a basically a hard particle like a little sphere but in fact what it looks more like is a wave that looks like that okay so this has certainly got a it's got an extent but you can see that instead of being just one being at one position which we could define here if we put X on this axis again so this is the position instead of just finding the particle at one position on the x axis we see that it spreads out it's got this wave like wave-like character for me and I think for many scientists nano scientists this is one of the key iconic images not just of nanoscience in the 20th century but of science in general it's it's it is really a huge impact and it's incredibly visceral it really is visceral this particular image what we have here the work was carried out by a group in IBM al-madinah and in the US and what they've done it they've positioned 50 atoms 50 iron atoms on a copper surface so this is an underlying copper surface and if they've used something we'll talk about Liat or I guess a scanning tunneling microscope which is a sharp basically a sharp tip you bring it in close to a surface you move it around and you can almost literally push these atoms around and so they form this ring of 50 atoms that in itself is a wonderful feat of atomic scale engineering but that's not what makes this image so beautiful what makes this image so beautiful is study it's like you took a stone and you dropped it in the center here and you can see these ripples of water electron waves spreading out and what it is is it's really visual and as I said visceral evidence of the wave-like nature of the electron because the electrons on this particular surface spread out like a basically a sea of electrons and as you're dropping effectively dropping a stone into that sea of electrons and what's remarkable is that you can use undergraduate first and second well second year undergraduate quantum mechanics to actually work out the separations of these rings the spacings of these rings

Channel: Sixty Symbols

Views: 55,092

Rating: 4.9770379 out of 5

Keywords: frequency, sixty, symbols

Id: PLey7TTGXTw

Length: 7min 2sec (422 seconds)

Published: Tue Apr 14 2009