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Transcript
WELCOME TO PROTONS FOR BREAKFAST MARCH 2010 WEEK 2: LIGHT 1 PfB12 Week 2 These are the questions & comments from Week 1 along with my responses. For everyone’s sake, I have removed any mention of people’s names. You said I said What makes Atoms make light. We will look at this more this week in both senses of light? the word ’look’ Mmmm. A perfect vacuum is a region of space without any matter in it. All Is gravity a vacuum? Oh, and the vacuums that we create actually do contain a few atoms, but the space can we have in between the atoms is a perfect vacuum. Gravity is a field which exists some cookies at throughout space, even in places with no matter. the break next We had more visitors than we expected. Steve went to top up the biscuits time? Please? during half time. We will make sure there are more next week Light is a disturbance of the electric field. But could If light is a disturbance in the electric field, could electrons and electrons and protons also be disturbances of another protons also be a ‘disturbance’. field? Quite possibly, but that is just too profound a Could they be ‘concentrations’ and question for me to answer in this space. ‘dilutions’ of the field? You like physics and chemistry? I thought that the physics topic was very interesting Great. I like atoms too. because I like space. I also like chemistry because I like atoms, electrons and really small things. ☺ Great Questions. But as even you know – they are If you know how big the universe questions without answers. Our current best estimate of is, what’s after it? Is there an the diameter of the ‘observable’ universe is 78 Billion edge? I wasn’t sure about this light years. However, the Universe it self must be much because my Physics lessons are larger than that, but we have no way of knowing how really boring! But is was fun and large. interesting. ☺ I am glad your mind is un-boggling because I will be I look forward to next week and boggling again tonight! the weeks after! My mind is un-boggling! It was an interesting lesson. You are very welcome. Thanks a lot. The best teachers are the ones you want to I think that is a compliment but I am not go back to. I am looking forward to more from sure! the Mad Scientist. Sorry, that’s how it is. Everything we eat and drink I don’t like the thought of drinking is electrical in the very core of its nature. electricity! Yes, those are powerful sparks. I was amazed at the holes were I am really sorry about your not doing enough formed by the electric sparks. I wish they would teach it like that at experiments. Ask your teacher if he or she would like to come along. school. WE DON’T DO The songs get better, and there are more each week EXPERIMENTS! The songs are bugging me now….. grrrr! ☺ 2 You said I said Main question: If the nuclides in a Mmmm I can see I am going to have to give you less time to ask questions ;-) nucleus are held together by a very strong short range force, Main Answer. Firstly I think the word you mean is why is it that this force becomes nucleons rather nuclides. ‘Nucleon’ is a collective word repulsive when the particles for either a proton or a neutron because their strong become extremely close under a interactions are very similar. I don’t have a particular -15 femtometer (10 m)? answer to this question – I just don’t know. However all forces have to behave something like this – attractive at Stream of thought/questions: Is ‘large distances’ and repulsive in some way at ‘short it accurate to call everything distances’. electrical? Everything contains particles which would carry a Stream of thought answer. current if delocalised. But maybe • Yes I think it is accurate to call everything I am thinking of current, where electrical. The physical properties of every the charged particles must be substance we encounter are dominated by the free to move about. Perhaps that electrical interactions between the atoms of which is why the word static electricity they are composed. Indeed our own bodies and is used, as it involves localised biochemistry are dominated by electrical charges. This electronic field is interactions. also intriguing. How can something • The word ‘static’ electricity is used because the that is not matter, interact with electricity is not ‘flowing’ as in an electrical current. matter, is it something to do with • Matter interacts with the three fields I mentioned. energy. In AS physics they talk • Do they really talk about W-bosons in AS level about transfer particles such as Physics? How depressing. These are words which can W-bosons and photons etc….. have very little meaning in that context. But how does this link to fields, if • I don’t think it is fair to say that ‘matter is a a field is a different entity that mystery’ when we know so much about it. There are somehow affects matter, surely of course many things we do not know. Each there must be some kind of force explanation of a property of matter has to be an which in turn is supposed to have explanation in terms of something else. At the end of particles which are in turn matter. a long chain of explanations there will always be a Although it could all be due to the few rather abstract ideas in terms of which many fact that matter is still a mystery many things are explained. to us? I am glad you and your children found it Have thoroughly enjoyed the first week – you enjoyable. You are very welcome. have made science fun. My very reluctant children had a great time and can’t wait for the next 5 weeks. Thank you. 3 You said • What determines if something is +ve or –ve charged? e.g. why does rubbing a balloon always create a +ve charge? • How does electricity ‘flow’? • How many ‘fields’ are there, and how do they interact with each other? e.g. is the electric field also the magnetic field?? I said • The type of charge on a balloon depends on what it rubs against. Whether electrons rub off a substance on to the balloon, or rub off a balloon onto the substance depends on the electrical forces attracting electrons within each material. • In a solid the electron ‘flow’ is a series of very fast hops between atoms. In a metal each hop takes only about 10-16 seconds, or 0.000 000 000 000 000 1 seconds. With so many electrons hopping so quickly, ‘flow’ is a fair term. • We know of three types of field, the gravitational field, the electroweak field and the strong field. They do not interact with each other at all – if they did we could work out if – or how – they were related to one another. However many people do believe that there is a relationship between these fields and are searching for a GUFT – a grand unified field theory, sometimes also called a TOE – a theory of everything. • The relationship between the magnetic field and the electric field fascinated people for ages – most especially Einstein who was inspired to create his special theory of relativity by considering the problem. I describe this relationship some way further down these notes. Yes. It’s called a vacuum. However there are fields Is there such a thing as nothing? even in that vacuum. Just there being nothing at all and no atoms. Plain nothing… Are there any good I like David’s Whizzy Periodic Table http://www.colorado.edu/physics/2000/applets/a2.html web-sites for understanding atoms? and I use web elements quite a bit http://www.webelements.com/ 4 You said I said • Absolutely. I don’t know why they don’t. Perhaps they could • So, when on paper also put a sticker saying ‘Genuine Big Bang Sourced electrons they put “made by oak only – guaranteed at lest 13 billion years old. trees” or whatever, they should put “made • I had no idea why spots come before your eyes when you are tired. But my wife told me they are well known phenomenon. by oak trees, and The NHS have a page about the phenomenon. atoms” instead. *Why don’t they? http://www.nhs.uk/conditions/Floaters/Pages/Introduction.aspx • Who do dots come before your eyes when . your tired? • Yes. Independent of whether the ‘source’ charge is positive • Will static electricity or negative, and whether the object being influenced is a attract everything? conductor or an insulator, the net effect is always attractive. • I love science but I • I have no idea how your phobia will affect you in later life. I have blood injury have heard it said that, whatever doesn’t actually kill you will phobia and you have to make you stronger. So your phobia can give you insights into do biology as well as how other people feel about other things. Can you think of it as a gift that you have to figure out how to use. It’s a physics and chemistry. strange gift to be sure, but a gift. We are undergoing a • No problem cure. Will it interfere in later life? • Although it is not a very scientific question, I hope you will accept it. I enjoyed getting a I have seen that film many times now and I am still amazed at just how better perspective big the Universe is and how tiny are the things in it. And also that over the years people have expanded their minds enough to be able to even of how big the universe is and how conceive of a Universe that big and particles so small. It hurts our imagination, but people have been compelled to these ideas by trying to small we are in understand what they see. relationship to it. Atoms are very very very very very small. That is very very very very very true. 5 You said I said • I am sorry: I can’t help it. • Excellent lecture and • Yes. It is a tremendous achievement at first sight it seems infectious enthusiasm impossible. In Week 2 we will see how people can work details for your subject. of the structure of atoms by looking at the light they emit. • I am as mystified as Similarly, people can work the structure of nuclei by looking to how people can at the gamma rays and particles that they emit. Working out know about the the size of the universe and the distance to stars has not unfathomably minute been an easy task. inside of an atom, as • What a profound question succinctly expressed. Knowledge is to how people can not a straight line progression. To be honest I don’t know know about the far what shape it is or how it evolves. Many people have theories reaches of space. about it (Thomas Kuhn and Karl Popper for example) which I • Is the knowledge a could only inexpertly summarise here. Occasionally people straight-line find that existing theories are just plain wrong – but more progression, added to usually they find they are limited in their area of in building blocks? Or applicability, and a new theory explains more, and more do scientists simply. It is inconceivable for example that our continually find that understanding of electricity and light is ‘wrong’, but it is prior theories were conceivable that it is in some way limited in a way we cannot wrong. In which case, yet comprehend. how can you know whether you are right? No. Gravitational forces are not electrical, and the “strong” force Are all the forces electrical between protons and neutrons is not electrical. in nature? What Please note that in this context the word “strong” is a name for the about gravity forces? force. We could have also called it the Feynman force or the Yukawa force after some of the scientists who studied it. At short range the force is also strong in the normal sense of the word Excellent. We all need a reminder from time to time. Tonight has They didn’t. It’s a fantasy – and put together in the crudest way – a series reminded me of 40 pictures were created and then a camera was moved away from the why I like picture to create the zoom effect. However the boldness and clarity of science. Thank the conception, and the focus on conveying a simple truth are still very you! powerful. The film has many shortcomings – for example at some point not How did the guys making the too far from Earth, the viewpoint apparently recedes faster than the speed of light – something which is physically impossible. An earlier version film know what attempted to communicate this, but in the end they just ignored this the view looked complexity. Sometimes, saying less communicates more ☺ like so far out from Earth and our universe? 6 You said I said • Excellent • What a great lecture. There was • Mmmm. Well it is important and it isn’t. No one will live or die as a result of any discoveries at the LHC whether they discover the a lot I understood Higgs boson or they don’t. But on the other hand it represents for the first time. one frontier of knowledge and understanding – the largest • Why is the scientific instrument ever constructed – and just a totally mindmeasurement of bending achievement. You should decide how important it is: after small things like Hicks (Higgs) all, you’re paying for it! particles so • The distinction between stuff and not stuff (which are not important? technical words by the way) is maintained even when things get • Do very big and very small. But very small entities do not obey Newton’s of very small things Motion; they obey another set of rules called ‘Quantum act differently or Mechanics’. do they all still • There are other basics too: but at the end of the 19th Century behave as stuff scientists thought they understood it all apart from a few and not stuff? ‘details’. I have emphasised the electrical nature of things • Is the basis of all because (a) it is true and you can immediately appreciate that; (b) physics electricity it is just not mentioned in current text books. But don’t get me or are there some started on text books!; and (c) understanding the electrical other basics too? nature of matter has huge explanatory power. That was also a periodic table. There is more than one way to reflect the What was the periodicity of the elements and I like that structure because its spiral table with elements on that structure reflects the ‘stacking’ of ‘shells’ of electrons. was next to the periodic table? I love them too ☺ Fun fly sticks. As I said above, there are lots of alternative ways of reflecting the Didn’t understand periodicity of the elements. the round Periodic Great table. Loved it though. Do electric (and magnetic Yes. They react at exactly the speed of light fields) react at the speed of light? Why do merchant bankers Advanced theoretical physics is hard but I can do that. Figuring out why bankers get bonuses and knighthoods is beyond me. get knighted as a matter Regarding my MBE, I feel I should be more cynical and sceptical, of course and you got a but actually I just feel delighted, and profoundly honoured. MBE? Surely should be the reverse! 7 You said What are electrical charges like for antimatter? What exactly is the Heisenberg uncertainty principle? I said Short questions with big answers. • Electrical charges for antimatter particles are the opposite of the charge for the equivalent matter particles. So an electron with a negative charge has an antimatter counterpart called a positron which has positive charge of equal magnitude. The electrical charge on a positron is exactly equal to the electrical charge on a proton • Small objects do not obey the same laws of motion as large objects. Their dynamics are described by the laws known collectively as ‘Quantum Mechanics’. One aspect of these laws is that it is not possible even in principle to know everything about a particle. For example, we might carry out an experiment to workout how fast an electron is travelling, but the more precisely we determine its velocity, the less precisely we know exactly where it is! The limit of the least conceivable uncertainty of measurement we can have on simultaneous measurements of position and velocity was calculated by Werner von Heisenberg. • Does that make any sense? I hope so. • I think you mean a ‘field free’ region • Can you make a “vacuum” of a field, i.e. a analogous to a ‘particle free region. enclosed space that has very little or none of Well it is possible to create regions the gravitational field or any other field. I’m where an electrical field is zero on guessing the simple answer is no, but why? average, but it is not absent! If you Supposing you could, what implications would could screen gravity then we could this have. have flying machines! • What if my favourite radio station is a DAB station!? • Even DAB has a frequency, but not • You should have the “This page is intentionally all radios display the frequency. left blank” paradox, get rid of the “aside from • Your wish…. this writing” bit (it’s funnier that way). • Ha Ha … • There are 10 types of people in the world. Those who understand binary and those who don’t. Errr….Thank you. I think? This was more interestingly quirky that Vector diagrams are quite tricky. But if you practice they do make sense. Do you have a particular problem or is just vector diagrams I thought it would be. in general? Question: Why are vector diagrams so hard A diode in general terms is any component with two leads. ‘ode’ is the Greek for a ‘way’. So di-ode is ‘two ways’. The thing that to figure out and distinguishes a diode from a resistor is that its electrical calculate in my mock resistance is different depending on which way it is connected in a exams? What is a diode and is it circuit. Electrons flow easily one way, but barely flow at all in the reverse direction. bad that I still don’t Is it bad you still don’t know? Don’t worry about it – everyone has know? big holes in their knowledge. Just learn and move on. 8 You said Good revision for me, very simple, easy to understand explanation. The introduction was a bit long, would have been more interesting to learn more about electricity. • Can you try and explain dipoles? We did it in chemistry but I was a bit stuck. • What is fire? I said I am glad you found it simple. Yes, the introduction is a bit long, but we will use these ideas over and over again in the coming weeks. • We will talk about dipoles – but I won’t really use the word explicitly. Why? Because it gets technical quite quickly. • Some molecules – such as water – have a built-in (or permanent) dipole moment. The exact reasons for how this comes about depends on the particular arrangement of electrons around the molecule. This affects the way the molecules move in an electric field, either applied by us or due to other molecules. For example below is a schematic illustration of a water molecule. When another water molecule approaches, it will feel forces that attract its positive parts to the negative parts of the first molecule. Many of the special properties of water arise from exactly this effect. Some molecules don’t have a built in dipole moment but can be polarised by an electric field either applied by us, or due to other molecules. If you imagine a spherical atom, then when an electric field is applied the electrons move slightly one way, and the nucleus moves the other way. So the centre of the positive charge and the centre of the negative charge are not in the same place: the atom has acquired a dipole moment. That was the process I tried to describe by which the piece of paper get picked up. • Fire is simply hot gas, sometimes with small particles of soot. In some parts of the gas the temperature is so high that atoms and molecules become ionised. In those regions the gas is technically known as a plasma. You can tell exactly the type of atoms and molecules in the flame by looking at the light it emits – more on that in the weeks 2 & 3 Wow! Well done. It gets very hard to return to formal Very please I have understood! studying in later life. It was worth doing a science Amazing – but true! I don’t know why people don’t GCSE at 52 last year! I had not really appreciated that emphasise this more. You are welcome. everything was affected by electricity before tonight. Thanks. • 9 You said I said Yay Physics indeed. Yay, physics ☺ Good • By the ‘other side’ do you mean the ‘inside’? I think you do. Well A-level revision. the answer is that no one knows. The concept of a black hole Could you answer involves the concept of a singularity – a point of infinite density. these? In physics there are no known examples of infinite quantities. - What is on the The Physics in this kind of region is beyond anything we really other side of a black understand. hole? • I don’t understand that question - What happens if 2 black holes face each • See above. And listen out in the following weeks. • Is it a liquid? I had not thought of it as so. I had thought of it as other? a dense plasma, but maybe a liquid is a good way to think of it. - What IS fire? (my Looking it up on the web’ the density in the outer part of the sun dad’s a fireman and he is roughly the same as liquid water, but the density of the inner can’t answer this well) part of the sun rises to 1000 times that of water – at a - Why is the inside of temperature of roughly 10 Million degrees celsius. the sun a liquid? • I don’t think there is a definite experimental answer for the (rather than a solid). shape of space-time. - What shape is space • A wormhole is an imaginary structure in space-time that somehow – is it a saddle or a connects one point in a universe with another point which is donut? apparently very distant in space and/or time. There is no Thanks ☺ evidence that any such structures exist or can exist. But it is not *Also (1 more) – What wholly inconceivable. is a wormhole? It is called Powers of 10. You can see it on You Tube as What is the video about the zooming in and out called because I would http://www.youtube.com/watch?v=A2cmlhfdxuY like to use it? If there are 70 beats of I am afraid it is only my supposition that the second is roughly a heart per minute then related to a heartbeat. But our heartbeat is our constant why are there only 60 companion and it seems plausible. seconds in a minute. It is indeed true, and the humidity of nearly 100 bodies in the That means a heartbeat lecture theatre caused the one I had to stop working. But when isn’t based upon a people went out for the break, the air conditioning managed to second. My science catch up and the experiment worked after the break. (Following teacher said that van de on from an answer above, I think the reason water is so effective Graaf generators work at conducting electricity in the air is because it has a permanent badly when it’s wet electric dipole moment) outside. Is it true? I am glad you like it. I think it gets better as we go on! The course is very, very good! 10 You said Are the electrons free on your jumper? from the outside of atoms of jumper. When did the electrons come vis a vis the Big Bang. Don’t the atoms in the air affect the field? I said No, not free – they are attached to atoms in my jumper. When the balloon touched my jumper, electrons right at the surface were pulled onto the balloon or the pullover depending on the electric forces in each material. Electrons were created along with protons in the first second or so after the big bang. I find that amazing all the electrons in my body are not merely 50 years old – but 13 billion years old! – no wonder I feel so tired all the time ☺ Yes, they do. But not very much. Except if they have a dipole moment (such as water) in which case they conduct electricity a bit more than dry air. Yes. Whether electrons are rubbed off an object or onto it depends on the electrical forces on the electrons near the surface. These vary depending on the detailed arrangement of atoms. The effect is known as the triboelectric effect and materials can be ranked in a series, called the triboelectric series. The series is very approximate, but allows you to figure out which way the electrons are moving when you rub any two materials. Read more here: If you rubbed the balloon (or something else) on something other than your jumper would it add (take away) a different charge to the outside of the balloon (or other object)? Is enthusiasm electric? Thanks for a very enjoyable evening. Origin of the Universe. I personally believe possible that the Big Bang theory as the start of everything has to be wrong. The explanation for the Big Bang surely is that matter gets attracted to Black Holes. Black Holes get absorbed into other black holes. Gravity gets stronger and stronger at some point the forces become unstable and a large explosion occurs. Where could I find out more about black holes and the big bang? http://en.wikipedia.org/wiki/Triboelectric_effect Errrr. I’m not sure. But possibly…. You are very welcome. Mmmm. Well that’s an interesting theory, but where is your evidence? The theory of the ‘big bang’ is constructed to match our observations. People have considered the question you have asked, but the question is “How could one tell?”. So they have asked questions like, if there was a universe before the big bang that was first crushed and then exploded, could we tell by looking for evidence in the world around us?” Currently the answer is ‘not really’ NASA has some nice sites http://nasascience.nasa.gov/astrophysics/what-powered-thebig-bang http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes. html For details try Wikipedia, but it is a bit advanced. 11 You said Why can’t atoms be enlarged so we can find out about them? They built a Hadron Collider so what’s stopping them? I said Atoms have a natural size which depends on the strength of the electric field around protons and the properties of electrons, particularly their low mass. People do take great interest in studying what are called Rydberg atoms, which are hydrogen atoms where the electron orbits the nucleus at a great distance – many times its usual orbit radius. Building the LHC is a stupendous engineering achievement. But changing the basic properties of matter is something which is beyond even our most advanced engineering. • Nobody knows. It seems likely but…nobody • Universe so large. Are there other really knows. life forms out there? • We will look at this in Week 5 – because that is • If the balloon/electricity affects the basis of the potential hazard arising from the “sausage”, how does the mobile phones. electric/radio waves affect us? • You are welcome • Great and enthusiastic speaker. • Yes, it is hard to avoid this concept of entire Thank you. universes within universes. • It seems that we are in the Universe and even the chaps hand (our bodies) are a micro universe. • Atoms are indeed made out of electrical ‘bits’ • Are atoms made entirely of (particles). The ‘solidity’ arises entirely from electrical electrical “bits” which forces between atoms. appear as solid matter – i.e. • I am afraid I am not going to explain the big bang – I is matter made entirely of can’t, but then neither can anyone else! As I mentioned electrical charges. above, it just appears to have occurred around 13 billion • Are you going to explain years ago. “the big bang” i.e. where did it come from? Electric thought. I am afraid I can’t quite follow that: maybe that is just what was on Glass for rear lights your mind. etc. I wasn’t aware quite how much electricity there really is Excellent. Most people are not and how significant it is in our every day lives!!! aware of that. I thought that it was excellent. I I am glad you enjoyed it. Thank you. liked the way it was presented. I am glad you enjoyed it. Yes, the Sun has loads of electrons. The mass of I really enjoyed the Sun is around 2 x 1030 kg. Most of this is hydrogen and a hydrogen this and learnt loads of facts. atom has a mass of roughly 1.6 x 10-27 kg, so there are roughly 1.2 x 1050 Does the sun hydrogen atoms – and so there are roughly 1.2 x 1050 electrons. That is a have electrons? really really big number! 12 You said I have? a lot of static electricity/charge – why is that? To date, I have blown up 6 toasters! 4 kettles! 1 iron and literally 100s of bulbs. It is also worse in summer – why? If I wear cottons clothes it does decrease and avoid polyester/nylon. Why does cotton have less or no static? I get loads of zaps from my car, earthing strips don’t work – what can I do? Please help. I said • Well firstly I don’t know. But the humidity of the air strongly affects the conductivity of the air. When the air is humid, triboelectric charges (i.e. charges separated by rubbing) leak away back to where they came form much more quickly than when the air is dry. So if it is worse in summer (when the air is generally drier) then the charges probably arise in this way. • No insulator is perfect, they all conduct electricity a little. Cotton conducts electricity much better than man made fibres, and also holds moisture longer enhancing the conductivity of nearby air. • Think about walking barefoot and avoiding carpets made with man-made fibres. Are your floors concrete or wood? Do you have good air flow? You could always try ionisers which reduce static build up. • Cars acquire a static charge because they have rubber tyres rubbing against insulating asphalt when they drive. I enjoyed the talk. I learnt many things on I am glad you enjoyed it. atoms and the sizes of the planet. • I don’t know what a gravity vortex is. I am not sure that such • What about a gravity a thing could exist. vortex? • Stuff and Non-stuff: YES! • Stuff (particles), Not • What a great question. This was amongst the toughest stuff (non particles). unanswered questions at the start of the 20th Century. • What stops the negative (in an atom) Eventually people realised that tiny particles do not obey going straight to the Newton’s laws of motion – called classical mechanics – like positive in the middle large particles do.. If they did every atom would instantly instead of orbiting? collapse as you suggest. Small particles obey rules called • With atoms, if you Quantum Mechanics. touch someone how • Well you do stick, just not very strongly. If two electrically come you do not stick neutral objects are brought close to each other (by close I to him/her? mean 1 nanometre), there is a weak attractive force between • What about wind? them, but this turns to repulsion when they reach a separation of around 0.1 nanometre. • Pardon me ☺ 1. All the physics that takes place on length scales ranging from the 1. How many diameter of the solar system to the size of an atom can be explained dimensions. assuming there are exactly three dimensions of space and one dimension 2. How many of time. If there were any more or less, we could tell experimentally. black holes. 2. I don’t know of even a single black hole that has been unambiguously identified, but there are many many candidate objects. I really enjoyed this class. Excellent. 13 You said I said You have been before? One key element of learning is I understood this more familiarity. Sometimes it just takes a little while for ideas to the second time of first become familiar, and then when they are familiar, they visiting. begin to make sense. One problem with learning is that it is often I now understand how hard to become familiar with new things – one tends to avoid absolutely everything is thinking about things which we don’t understand. electrical. If you understand that everything is electrical then you have a Hopefully a few topics at profound insight into the world. school will make sense I hope so☺ now! Excellent. I have learnt that I am glad you are not confused about the size of the universe. everything is electrical. Not so confused about the But confused or not, its hard not to be at least a little boggled!! size of the Universe. • Yes. Can sand get • At first I thought you were asking whether things could be lifted by the lifted by a buoyancy of the balloon, which case the answer is this: A helium balloon balloon? with a volume of one cubic metre has a diameter of roughly 1.3 metres Can we lift and (neglecting the weight of the balloon itself) can lift about 1 kg of our own food. sand (about half a litre of sand). • But when my wife read this she said she thought it was a question about whether a balloon could lift a particular weight electrostatically. The answer is still yes, but the weight that can be lifted depends on how much electrical charge there is on the balloon. But with enough charges, you could lift anything. Its tricky. Early measurements made by a scientist called Michelson worked How do you like this. A bright light was shone onto a rapidly rotating mirror onto a measure the distant mirror – perhaps one kilometre away. The light was reflected back to speed of the rotating mirror. The round trip takes roughly 7 microsconds. If the light? How accurate mirror rotates 100 times per second, then it will have rotated roughly one quarter of a degree when the light returns and the image of the light will can you appear in a different place. By measuring the distance the light travelled and measure a knowing the speed of rotation of the mirror, the speed of light can be metre to? measured by measuring the deflection of the image. Nowadays we don’t measure the speed of the light – we define it to be a constant and use it to work out distances and times. We can pretty easily measure one metre to 0.000 1 millimetres. More accurate than that gets a bit tougher. 14 You said How did scientists discover that there were fields i.e. that the world is not just matter? I said Great Question. Ignoring gravity for the moment, people spent a great deal of time trying to understand the nature of electricity and magnetism, and quite separately, of light. There were many nascent attempts to imagine how magnetic and electric phenomena affected distant objects. But in the middle of the nineteenth century, all the pieces came together. It was a combination of new experimental results and new mathematical techniques that made it possible. James Clerk Maxwell was trying to understand how electric forces (like those from the balloon) were communicated across space. He constructed a theory which posited that something existed in the space in the absence of matter (they called it æther). He worked out what speed waves in this ‘field’ would have and found – to his astonishment – that the speed was exactly the same (within a very small uncertainty) as the measured speed of light. In his journal he wrote that this ‘could not be a coincidence’. This was the first modern field theory and it was essentially perfectly constructed at the outset. About 50 years ago Richard Feynman modified the theory to explain how light waves are emitted and absorbed in finite ‘chunks’ known as photons. Can you crush a Yes. But we can’t exert such strong forces on Earth. In certain stars known as neutron stars, the gravitational field is so strong that atoms are crushed atom? and the electrons are squeezed into the nucleus and – using physics that is Could a wave way beyond this course or frankly me personally – the electrons combine affect the with the protons to make neutrons. And the stars consist of pure neutron earth or the matter, roughly one million million times denser than any substance on earth’s Earth. atmosphere/ Yes. Waves of all kinds affect us all the time. We will look at some of this in Week 4. When can I meet the elderly, presumably Oh. Sorry we have other Robert Goddard helping retired, white haired rocket scientist you have helping out as a helper? http://en.wikipedia.org/wiki/Robert_H._Goddard Your “helpers” slide showed Robert Goddard as a helper. There is a lot of it about, but separating it from matter to I didn’t realise there was so make useful electrical power is still quite a trick. much electricity hanging about You are welcome – I thought we had to do more to make it! Thanks a lot. Excellent. Very It depends on the type of light bulb. In the simplest type of light bulb, interesting! there is a filament (a thin wire) of tungsten – an element which does not Q. How is melt until 3422 °C. An electric current flows through the wire and heats it electric to an astounding 2500 °C! At this temperature, the light bulb gives out lots converted to of electric waves, some of which are visible – light! We will talk more about light in a bulb? how this comes about tonight and again in Week 3. 15 You said How do atoms of the same type (e.g. H) ‘attract’ each other to form molecules when they both have – charges on the outside. I said Great question. The atoms may be neutral, but the electrons are not uniformly arranged around the outside of the atom. Atoms in which the electrons are uniformly arranged the outside of the atom (Helium, Neon, Argon, Krypton, Xenon and Radon) do not form multi-atom molecules, and indeed barely react chemically with anything else. On other atoms the electrons are not uniformly arranged around the nucleus. That means that other similar atoms can ‘see’ the charge on the nucleus. For the person who asked earlier – the atoms form an instantaneous electric dipole. And this can electrically attract other atoms or molecules. The electron was ‘discovered’ by J J Thomson. People had investigated Who discovered electrical charge the ‘rays ‘ that could be drawn from a negatively charged piece of metal called a cathode in side a glass tube which had most of the air removed. of Protons and The devices were called cathode ray tubes. Thomson performed a series electrons and of experiments that showed that the rays were streams of how? extraordinarily light particles with a negative charge. The story of the discovery of the proton is more complex, but the key figure was probably Ernest Rutherford. You can read more on Wikipedia here: http://en.wikipedia.org/wiki/Proton#History I don’t know if the Universe goes on for ever. And although Does the universe go on there is much speculation on the matter, I don’t think there is a forever? Because otherwise if it ended what really definitive scientific view on the matter. would be outside it? Yes! Atoms in the air and within our body are Are we not affected by the constantly jiggling. If the jiggling gets too intense (i.e. constant pull and push of atoms if the air or our bodies become too hot) then we indeed around us. cannot cope! More in Week 3 How does our body cope with this? It was very fun but maybe we could have maybe 15 Mmmm. It’s a balance. In week 2 you mins more time to use all of the amazing have 5 more minutes! And Week 3 is a experiments? bit more relaxing. But I really enjoyed it and learnt a lot and also I am glad you enjoyed it. thought he was very good at what he did. Thnx. Excellent. Yes it can be disconcerting I was fun and interesting and I learnt a lot. sometimes to think about just how small I liked watching the experiments. It made me some of the things in the world are, and realise how small everything in the world is. a just how big is the Universe in which It helped me understand a lot more of what I we live. know. You are welcome. I enjoyed the videos. Thanks. Time travel – how could it Aside from my regular trawl through time, I know of no way of be done? travelling through time. 16 You said I said Why are Bourbons more attractive Chocolate. We will try and have more next week. You are welcome than Digestives? Thanks. The Greeks could not see atoms (except in the same way that we all see How could the atoms all the time). Sometime around 450 BC Democritus reasoned that if Greeks see atoms to know one kept dividing a substance into a smaller and smaller parts one would that they eventually arrive at a particle which could not be cut (literally an a-tom). couldn’t be cut? In this original conception, stones would be made of atoms of stone and fur would be made of atoms of fur. The idea was that these atoms were indestructible and merely recombined to make new substances. So some of the key ideas of our modern concept of atoms were there, but also several key concepts were missing. The reasoning at this time was speculative – our modern conception of the atom is very much based on factual evidence. You are very welcome. I am sorry to hear My Feedback: that your Friday lessons are I’m in year 8, and I’ve learnt more HERE than in disappointing, but glad you enjoyed the my Friday lessons! I learn in my Tuesday lessons, but not so much on session. Well you can test the pencil! Hang it up my Friday one! This has really helped. Thank you by a thread tied around its middle and very much. Everything is electric? REALLY. Even this pencil? see if you can attract it with a balloon! Yes, the atoms and molecules in the air are affected, How does the charge on the but only weakly. In each cubic centimetre of air there balloon induce the charge on the are roughly speaking only one thousandth of the number paper through the air i.e. how do of atoms and molecules as in 1 cubic centimetre of any the atoms in the air between get solid or liquid substance. affected – is a charge induced in the atoms in the air as well? Why does it make a Whether electrons are rubbed off a material onto a balloon, or off the balloon onto the material depends on how strong the electrons are difference what sort of material you attracted to the atoms of the rubber and the other material. This depends all kinds of complicated details of each substance. The rub the balloon on i.e. cotton, wool, etc. roughness of the surface will also make a small difference. There is a reasonably well documented series called the triboelectric series Does the surface make a difference which says which things rub electrons off which. The list si below, for i.e. smooth, rough, what its worth. knitted, woven. http://www.siliconfareast.com/tribo_series.htm 17 You said You mentioned Fields - Gravitational - Electroweak - Strong. Not heard of them before, what are they? Heard of electromagnetic . I said Protons affect other protons through all three fields. If a proton moves then: • The gravitational field is disturbed because protons have mass. A short while later when the disturbance reaches other protons they will move in response. • The strong field is disturbed because protons have another property about which I have not told you (!). The disturbance doesn’t travel far in the strong field. A short while later when the disturbance reaches other protons they will move in response. Because the disturbance doesn’t travel far, protons only affect other protons through the strong force when they are very close. • The electroweak field is disturbed because protons have electrical AND charge. A short while later when the disturbance reaches other protons they will move in response. What is an We have described the electrical aspect of the electroweak field. electroweak and However there are also a ‘magnetic’ and a ‘weak’ aspect. We can see the a strong field? connection between electricity and magnetism fairly easily. (ish) • When an electrically charged particle affects another electrically charged particle through the electroweak field we call the interaction electrical. • If the either particle is moving we still describe the interaction as electrical. • However if both electrically charged particles are moving (e.g. in two wires), we describe the interaction as having an additional magnetic component. However, if we imagine travelling with one of the charged particles, then it would appear stationary, and we would then have describe the interaction as purely electrical. Considerations such as this led Einstein to formulate his Special Theory of Relativity which allowed us to understand that magnetic interactions are really just ‘How electrical interactions look when charged particles are moving’. The ‘weak’ interaction is more complicated to describe, and if you will forgive, I will not do it here. Again the word ‘weak’ is just a label describing a short-range interaction between particles which is not the ‘strong’ interaction. The connection between the electromagnetic and the weak force was only discovered in the 1980’s. By this question I assume you mean Einstein’s General Theory of Do you understand relativity. If you do then the answer is indeed ‘No.’ I suspect the gravity? My brother answer is many more than 10 – nearer 1000 or so, but indeed that is said only about 10 still not a large number. people do? 18 You said In outer space is the majority of space matter or a field? I said In outer space there is only a single atom (usually hydrogen) in each cubic centimetre of space. So the most of the space is filled with ‘fields’ rather than matter. In contrast, in the air around you now there are roughly 1019 atoms in each cubic centimetre. 1019 is 10 000 000 000 000 000 000 atoms. –ish. I’m finding the course very informative We have lots, lots more to show and tell. And and can’t wait to learn more! more songs too ☺ • Its something else! Electric charges don’t affect the strong field. • What was However some particles such as protons and neutrons have other the properties (which I haven’t really discussed) which do affect the strong difference field. Thus when a proton moves it disturbs not just the electric field, between but also the strong field and the gravitational field. Although protons electric repel each other electrically, they attract each other through the fields and strong field. However unlike the disturbance to the electric field which ‘strong’ extends for a long distance through space, each proton only disturbs the field – if strong field for a very tiny distance around itself. This makes the strong isn’t electric – strong interaction between protons essentially a contact force. The what is it? strong force acts roughly equally between protons and neutrons – it just • How can we doesn’t ‘see; the electric charge the particles possess. measure • Measuring the distances to planets and stars and galaxies is very space? (per difficult and it is a triumph that we can do it at all, even though there the film?) still uncertainties involved in our estimates. For relatively nearby stars, • Thank you. we can work out how far away they are by looking at them against the background of more distant stars at different points on the Earth’s orbit around the Sun. We can detect tiny differences in the apparent position of the stars and knowing the diameter of the Earth’s orbit we can work out the distance to the stars. http://heasarc.gsfc.nasa.gov/docs/cosmic/nearest_star_info.html There are other tricks for finding distances to more remote stars. We have studied nearby stars called Cepheid variables. The absolute brightness of these stars varies every few days, and the period of the variation is longer for brighter stars. If we spot such a star in a distance galaxy we can measure its period, and infer how absolutely bright the star is. By measuring its apparent brightness we can work out how far away the star is. http://starchild.gsfc.nasa.gov/docs/StarChild/shadow/cepheids.html I told you it was complicated! • You are welcome 19 You said I said To the best of our knowledge all protons have exactly the same value of Do all protons have the same electric charge. They have also checked that electrons have exactly the level of opposite value of electric charge. People have checked this very carefully. electricity? As I think I mentioned somewhere above. When the You touched on role of valence electrons in chemical reactions. electrons orbiting an atom make a perfectly spherical Example given was two H atoms pattern around the nucleus then the atom is chemically unreactive. This is called ‘completing a shell’ by chemists. In combining to give H2 molecule. other atoms, the outer (valence) electron shell is not But if electrons have same complete – that means that the other atoms can detect charge you might think they’d some of the electric charge on the nucleus and are repel. Does this mean that the valence electrons are important attracted to the atom. Once the atoms get very close the electrical forces become very strong, and coupled with the for some reason, but that the unusual dynamics of small objects (called Quantum full story must involve the mechanics) the electrons adopt new orbits in what is called protons also? Any insight into a ‘chemical bond’ why valence electrons are so chemically important? It is a very confusing term. In a sense every chemical reaction ‘splits’ atoms What does because takes or adds electrons away from atoms. However the phrase splitting the would be more correct if we spoke of splitting the nucleus of atom. atom mean? This can be done in a number of ways, but typically, it involves bombarding a substance with protons or neutrons or even entire nuclei of other atoms. Most of the particles don’t hit nuclei in the target but some do, and by interact electrically and through the strong force they can break up a nucleus. Technologically the most important case is the fission (the scientific word for splitting) of some atoms of Uranium. Addition of a single neutron causes the entire nucleus to split into two or more parts. The fragments move enormously fast and release tremendous amounts of energy. The process is at the heart of both nuclear power and nuclear weapons and we will look at it more in Week 6. 20