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PROTONS FOR BREAKFAST SPRING 2013 WEEK 2 LIGHT 1 This is what you said on the feedback forms in Week 1 You said… Michael said.. You have obviously I do indeed have a vast library of songs and recently got a vast and they have become available on iTunes. Details here: fantastic library http://protonsforbreakfast.wordpress.com/songs/ of science songs. but don’t look if you want the songs to be a surprise Please could you each week . provide links to Somewhere else in these notes I described how in them. magnetic materials the electrons orbiting around one Why are there atom orbit in the same sense as their neighbouring only 3 magnetic atoms. So lots of electrons all orbit neighbouring elements? What atoms in exactly the same way. The conditions that makes them allow this kind of ordering are quite rare so magnetic magnetic? Will you behaviour is not very common. Iron, Cobalt and Nickel be explaining are strongly magnetic at room temperature, but in magnetism again? Week 3 we will see how temperature affects Are the fields magnetism. made up of No, fields are not made up out of particles of ‘stuff’. electrons? We will look at this again this week. And demonstrate the nature of fields with Jelly babies. It is fascinating learning Fascinating and shocking. It is difficult to about the power of ten and feel comfortable in a Universe that is quite that is a mere speck in the so disturbingly large. universe. I don’t think so, because I have never come Is the universe infinite? across anything in physics which is infinite. I It is a quantum fluctuation! think infinity is just a concept in (I think that is sciency mathematics. language for nobody knows.) Didn’t I say that? It sounds familiar! But I I learnt loads and this only am glad you learned a lot. the first session! But what I am afraid protons don’t eat but they must protons do we eat for be hungry! They were all formed between 3 breakfast? minutes and 20 minutes after the big bang – And what is your favourite and they haven’t had a meal since! periodic element? My favourite element? Tricky. I think it is Loved the talk and can’t probably potassium which I studied in great wait till next week!. detail for my PhD. More recently I have studied argon a lot but we haven’t really grown to be friends. It’s here already! 2 You said… Michael said.. We already knew about the experiments It is difficult to get the balance or had been shown them before hearing right for everyone. The idea of your lecture, so probably it would be having things available beforehand more interesting if we got to observe and at the break is that the meaning other experiments (on that same concept of what you see may have changed. of course) or they were not displayed We try to keep things simple and before your lecture. social. In the break you can talk to The delivery style is very lucid and other people, or helpers. Or me! I entertaining and attempts to kindle think it is very important to link interest and keep one listening in a together theoretical ideas and very positive way, so great job Michael, keep mundane experiments and understand on going!! the relationship between them Glad you like the style – I have no choice about it! How were Simple question complicated answer. I think it was the atoms culmination of a large number of observations many of which you discovered can make for yourself. Here are some: within Leave out a saucer of water in your home and the water will everyday disappear! (We say it has evaporated) objects? If you chill the now empty saucer, then water will reappear on its surface (We say it has condensed). If you cool water further it changes from being able to flow to forming a rigid shape. And then on warming it regains the ability to flow. (We say it was frozen and melted). Thinking about all these common properties of water – what could possibly be its microscopic structure? However going from this kind of insight to a theory with different types of atoms took hundreds of years. It is not at all obvious. Great introduction to Thanks. More adventurous? What an interesting the nature and expanse comment. Do you mean I could have added more detail? of science. Could have Well it’s a difficult choice. I can add more detail at the been a little more expense of a song. Or at the expense of repeating adventurous with the something. Or a demonstration. Intellectually I think explanations. the course is really quite ambitious. And it is intended to be for everybody. See how you feel after this evening’s session! 3 You said… 1. Why, if string theory is hypothetical, does it not become proven conclusively by the discovery of the Higgs Boson, which majorly proves the Standard Model, and thus most aspects of Type II superstrings? 2. Electricity would be strictly classed as electromagnetism, so what are the core concepts of the initial equations of Grand Unified (Theories) – for example, in the relativistic massenergy equivalence formula, energy = mass times the speed of light squared, so how do the GUT equations equate these variables. 3. Could you please explain the de Broglie hypothesis? Michael said.. 1. As understand it, string theory has no predictions about any of the discovered particles. It is describing physics on a much grander scale and all of the physical reality we observe – protons, electrons, atoms etc. – is just a detail. The Higgs boson is indeed a feature of the Standard Model but the standard model has nothing to do with string theory. Many scientists consider string theory is not just hypothetical, but that it is so detached from reality that it can never be demonstrated to be either wrong or right. Time will tell. 2. As I mentioned, we now understand magnetism is not separate from the electric field, but is just how the electric field looks to us when charged particles are in motion. So electromagnetism is a ‘unified’ theory – one theory explaining two categories of phenomena – electric and magnetic. Similarly we used to think that there were two distinct kinds of nuclear force called the weak nuclear force and the strong nuclear force. However now we understand that the electric force and the weak nuclear force are simply different aspects of one force which we call the electro-weak force. Many scientists believe that there must be a connection between all the forces we observe electro-weak, strong nuclear, and gravitational. Such a theory is called a grand unified theory (GUT) . However although people have tried to construct such a theory, none have been successful. 3. In the 1920’s Davidson and Germer in the USA demonstrated that electrons could be diffracted and so behave like a wave. Louis de Broglie (a PhD student!) tried to understand how electrons could sometimes behave as a particle and sometimes as a wave. He hypothesised that the particle is accompanied by some kind of a ‘pilot wave’ that guides the particle where to go. He imagined that this pilot wave could be diffracted, and then guide the particle to an unexpected position. He then calculated the wavelength of the ‘pilot wave’ in terms of the momentum of the particle. This particular theory isn’t widely held now, but gave rise to Schrödinger’s Wave Equation which essentially replaces Newton’s Laws when talking about the laws of motion of small particles. 4 You said… What happens if you split atomic particles? Is light a wave or a particle or both? Michael said.. It depends what you mean by ‘atomic particles’. Splitting atoms is common – we took electrons off atoms using the balloon and so made ions. But what people normally mean by ‘splitting atoms’ is splitting the nucleus of an atom. Suppose we have a heavy nucleus such as that of uranium. A uranium nucleus has 92 protons and typically ~146 neutrons. If it is split by disturbing it in some way – such as firing a neutron into it, the nucleus will split into (typically) two large chunks and several smaller chunks. Each piece of debris containing protons will form the nucleus of a new atom – and the number of protons in each piece of debris determines the type of atom i.e. which element is formed. Suppose a nucleus split into three chunks with 40, 45 and 7 protons respectively. These would form nuclei of zirconium (Zr), Rhodium (Rh) and nitrogen (N). Each nucleus would gather around the matching number of electrons to make the atom neutral. Each nuclear chunk would have a slightly random number of neutrons because of the chaotic nature of nuclear split. This will make the nuclei unstable – and bits of nuclei will then be ejected in a process known as radioactive decay – more in Week 6. The fundamental nature of light is whatever it is, but we notice that: o Light is emitted by single atoms in a single place o Light travels through space as a wave o Light is absorbed by single atoms in a single place Technically we can describe this as the creation of a particle (called a photon) and its subsequent annihilation. Personally I think that although it is technically correct, at the level we are discussing the world the description is misleading. Most people think of ‘a particle’ as a ‘thing’ or as ‘stuff’. But a photon comes into existence when an atom vibrates, and then pops out of existence when it makes another atom vibrate. That doesn’t sound very particle-like to me. I think in almost all cases the classical description of light is closer to reality. To answer your question, light is light, and sometimes it behaves a bit like a particle, but mostly it behaves like a wave. 5 You said… Michael said.. Interactive. Interesting. Mmmm. Is that an instruction to “Make Science Mind blowing. Make science Easier to Understand !” or a statement that that easier to understand. is what I am doing? Either way I will do my best! Really enjoying the storylines. I teach Really glad you are enjoying the science (physics) and it’s fascinating to course and that you are tuning in to hear how well the story connects when the story. The basic story of physics there’s a bit more stretch included. Very is very simple and very compelling. enjoyable – can’t wait until my 2 boys are And every time I re-tell it, it is like old enough to come. discovering it again. If there are loads of Since people developed telescopes capable of galaxies then how do we spotting planets orbiting other stars they have know that there is not other discovered hundreds of planets and it is clear intelligent life-forms? And that planets of all types – large and small, hot do you think that there are and cold, wet and dry – are common throughout other intelligent life-forms? the Universe. Given such a wide range of Is it possible that there may planets I think most scientists would expect be life-forms on planets like life in some form to exist on some of these Mars and the moon and the planets. other planets in our solar Even on Earth we find it hard to categorise system and universe that exactly what is living and what is not. So for don’t breath oxygen or example, viruses are considered to be on the survive on liquid water and border of the inanimate. Life on other planets glucose? and I’m not asking could be (and no joke intended) completely about bacteria. alien, and we may not even recognise it. It Shouldn’t Protons for might respond to its environment much slower Breakfast be called Protons than we expect and so appear inanimate to us. for Dinner (because it’s Well I have thought about the name and I dinner time (7:00)). Great thought the words ‘protons’ and ‘breakfast’ job, really interesting. Love went well together. I think it is because the tea. breakfast is perhaps the most personal meal of the day. Glad you are enjoying it. Very interesting. Changed my outlook on “stuff”. Excellent! 6 You said… Very mind boggling things! How do scientists make microscopes see so far? Michael said.. It is indeed mind boggling. One of the great ‘tricks’ that scientists use is this: They write down what they did and publish it in scientific ‘journals’. This saves people from having to spend a long time re-discovering stuff. So that if one person builds a microscope or telescope one way and describes what they have done, someone can read it and then maybe try a different technique. So modern telescopes and microscopes in all varieties are built on hundreds of small insights and tricks along with the occasional stroke of genius. Think about a modern car – it is enormously better than the cars built in the 1960s, but those improvements came gradually even though many were obvious. Cars are now faster, cheaper, lighter, quieter, and more fuel efficient. It is the same with scientific instruments. BY reading about what other people have done we can make progress without having to waste years following a dead end. What is gravity? Gravity is a force which we observe between any objects You said you didn’t with the property of mass. Newton calculated the know why it works. properties of gravity and realised that exactly the same But great talk. Even force which pulled an apple to Earth, also made the Moon I got most of it, and orbit the Earth. An amazing insight. I was only here for After 300 years of thinking that Newton’s vision was the my grandson. last word on the matter, Einstein then noticed further incredibly obvious things about gravity, and developed his breath-taking general theory of relativity. It is Einstein’s modern theory that I don’t understand. I hope you and your grandson enjoyed yourselves. Thanks for sharing the fun I am glad in my heart that you enjoyed it: with us! I loved it. Paper is full of Ha Ha! No. To me the greater miracle is that most things atoms, is that why don’t get lost in the post – but then I am not the best letters get lost in organised person in the world. the post? Why does The aluminium stuff was a thin layer of Mylar plastic a balloon gradually coated in aluminium. On the balloon or the Mylar shape slide off the wall, there is a concentration of electrons which are repelling when that very fine each other, but they can’t move because they trapped on aluminium stuff an insulator, and the wall is an insulator too. But nothing is does not? a perfect insulator – and eventually the charges repel each other and the electrical attraction to the wall is reduced. Balloons weigh around 10 grams but the Mylar shape probably weighs less than 0.1 g. So it takes much less charge to hold up a piece of Mylar than it does a balloon. I think the Mylar shape will fall to Earth eventually. 7 You said… Is a light year is the time that takes light to travel in 1 year? The distance that 1 light year is calculated to be 1016 (more or less)? How long would it take us to travel to that point where light originates from. Would we ever reach that point of origin. Michael said.. Ahhh. A light year is not a time, but a distance. Light travels through a vacuum (or air) at around 3×108 metres per second. i.e. 300,000,000 metres per second. So: in 1 second light travels 300,000 kilometres in 1 minute light travels 60×300,000 kilometres = 18,000,000 kilometres (18 million kilometres) o This distance is a light minute in 1 hour light travels 60×18,000,000 kilometres = 1,080,000,000 kilometres. Or 1.08 ×109 km. Just over a billion kilometres. o This distance is a light hour in 1 day light travels 24×1.08 ×109 km = 25.92 ×109 km. Nearly 26 billion kilometres. o This distance is a light day in 365.25 days light travels 365.25×25.92 ×109 km = 9.5 ×1012 km. o This distance is a light year To find the time to travel to the point where light originates you take the distance, and divide by the speed of light. So for the light bulb in your room which is 3 metres away, then the time taken is 3 metres divided by 300,000,000 metres per second Which is 10-8 of a second, or 10 nanoseconds. During this time your computer with a CPU operating at 2 GHz could do 20 calculations. What is an I don’t know. I have never heard of an electrostring electrostring force? force. Sorry. Or was that electro-strong? We don’t know Is there a weak of any connection between the strong force and force? So many electricity. questions! This is Yes there is a force called the weak nuclear force. It’s a very relevant to my bit complicated to describe here, but we now know that it physics and is related to the electric force. chemistry GCSE. I am glad you are able to make the connections to your GCSE It was fun, interesting, and I learnt a lot. I am glad Fun, lively and very interesting. Great. I am looking forward to it too. I look forward to next week. 8 You said… Question: When the big bang happened there was a massive outward force that is meant to still slowly be happening. If so in a certain period of time will this force the earth apart into the original chunks that collided together to create the big bang theory. Feedback: Personally enjoyed very much the way you gave the information because it kept me interested and made me really question what I know, which really helped me remember all the things you said and all the things I learnt. The demonstrations you gave I have seen before but I felt that the way you showed and explained them helped me understand and enjoy seeing it again. Michael said.. Answer I don’t think so. There are three aspects to the way the universe grew (and is still growing) after the big bang In stage 1 the Universe is thought to have undergone ‘inflation’. This very short phase began roughly 10-36 seconds after the big bang and lasted until roughly 10-32 seconds i.e. it lasted for roughly: 0.000 000 000 000 000 000 000 000 000 000 1 seconds During this time, the Universe is thought to have grown by a factor roughly 1030 in size for reasons that nobody can explain. After this ‘inflationary’ era the universe grew for two reasons. One was the explosive momentum we can all imagine from any explosion. This force won’t tear the Earth apart because the explosion is pretty quiet now – it has been 13.5 billion years or roughly 4.3 ×1017 seconds since the big bang. The other expansion was the expansion of the space in which cosmologists imagine the matter of the Universe resides. So although it is only 13.5 billion years since the big bang and matter cannot travel faster than light, cosmologists estimate the universe is around 78 billion light years in diameter. The difference is due to the expansion of space. This expansion too is rather tame now and will not tear apart the Earth. Glad you enjoyed the demonstrations. I still enjoy each of the demonstrations no matter how many times I have seen them before. Mind boggling. Indeed – but I hope you were able to cope? Fantastic enthusiasm from Michael. Glad you enjoyed it. The second half was a Coffee break could be short (say bit a rushed: sorry – it isn’t normally, but I 15 mins), and last ½ hour felt am not sure why it was this week. In Week rushed (so much fascinating stuff 1 the break is relaxing but we have more to take in). for you do next week! Had a really great time, it was pitched at the perfect Glad you enjoyed it. level for everyone, and not too much info at once. 9 You said… Why do you get random electric shocks? Do you get headaches as a result of atoms/electrons etc. in the atmosphere? Why did people think electrotherapy would help people with mental problems? Explain the science behind it. Michael said.. I think you are talking about the electric shocks one often gets in offices or sometimes on exiting motor cars. The processes that cause these shocks are complicated but the main culprits are electrical insulators. In the natural world, very few materials are good insulators. Amber is one of the few and that is why everything to do with electricity is named after the Greek word for amber elektron. The rubbing that I used to charge the balloon is a very common process – every time you walk or your clothes rub against something, charging takes place. With natural materials, the charges can find imperfections in materials that allow them to move away from each other, and so with natural materials we tend not to get such strong charging effects. The modern materials that we use in our clothes and in carpets and constructional materials are made of plastics which can be fantastic insulators. When we place charges on their surface, by walking or rubbing, the charges can’t escape. So walking on a carpet we can lose electrons and then a few seconds later when we touch something we get a shock as some electrons in the door handle (they get everywhere!) jump the gap and stimulate our nervous system, which is also electrical. I don’t suffer much from headaches, aside from the wellunderstood effect of carbon, oxygen and hydrogen atoms arranged to make C2H5OH - ethanol. I can’t explain the science behind electrotherapy – electric shock therapy – because I don’t think there is much. The widespread use of electric shock therapy – in which large electric currents were passed through people’s brains as treatment for mental disorder – seems like a shameful episode in the history of medical science. 10 You said… Comment: Very good lecture. Question: I know you didn’t want to get into it, but does electrical charge create permanent magnetism in metal (iron)? Michael said.. Glad you enjoyed it Permanent magnets are complicated. We will say a little bit more about them in Week 3. The magnetism in materials like iron arises from two sources, one of which is well understood, the other not so much. As I mentioned electrons ‘orbit’ atoms and so motion of the electron in some orbits is like a tiny loop of electric current. The motion of the electron has no effect on stationary charges, but we describe its effect on other moving charges as a ‘magnetic’ effect. Thus in some atoms each orbiting electron behaves like a tiny atomic-size version of a bar magnet. In a few materials the electrons naturally arrange their orbits so that electrons orbiting on neighbouring atoms all go around in some sense. Why? Because it minimises electrical repulsion between electrons on neighbouring atoms. But this means that the magnetic effects of lots of atoms add up – like lots of tiny bar magnets lining up. The force causing the alignment is straight-forward electrical repulsion. As you may know when you try to line up bar magnets the same way around – they tend to try and flip the other way. In a normal piece of iron, the atoms are nearly all aligned with their neighbours, but the direction of alignment changes from one region to another. Typically the volumes where the atoms are aligned (called domains) are around 0.001 mm in size. Making a permanent magnet out of iron involves a number of tricks for getting the domains to align (such as applying a big magnetic field) and then stay aligned when the aligning field is removed (such as damaging the crystal structure by beating it!) Like I said: it’s really complicated. 11 You said… Michael said.. A question: Is Mmmm. Very interesting question but I am not quite sure what there any way you are getting at. I can think of two possibilities depending on to measure the whether you had in mind gravitational fields or electric fields. ratio of mass The gravitational force on an object depends on the object’s and fields in an mass. So the ratio of mass and gravitational force will just be a area? Is there constant that tells us the strength of the gravitational field. any variations Or alternatively, according to Newton’s second law, the at all? acceleration of the object. A comment: Or are you asking whether the electric field affects the mass Best lecture of an object? I have never come across anything to suggest ever seen as it that might be true. If I have got hold of the wrong end of the was both stick please ask me again! educational and Glad you enjoyed it. I am blushing funny. A completion of my knowledge A completion?! No, more like a taster! You could of electricity and magnetism. spend your entire life studying this and still find phenomena that would surprise you! What is ‘dark ‘Dark Matter’ is matter that astronomers believe exists all matter’? around us but which we cannot see or detect except by its Absolutely gravitational effect – except in our laboratories we can’t even fascinating detect that!! Why do astronomers believe it exists? Because presentation. when they look at stars in distant galaxies, they see that they Captivating. are bound into the galaxy with a gravitational force which is Many thanks! too strong to be accounted for by the matter they can see. Now you or I might say “Mmm, that’s curious, there is something we don’t quite understand about galaxies”, but astronomers are bolder than you or I. They say “We understand everything about distant galaxies therefore there must be some “Dark Matter” present giving rise to the gravitational field.” Nobody knows what this consists of or even if it really exists, but that has not stopped reams of speculation. Time will tell! 12 You said… Michael said.. When the ‘fields’ Great question. Yes. The Dutch Metal device was called a (protons from the Gold-Leaf electroscope and its response allowed us to balloon) react with measure the strength of the electric field. This is the sausage – there modified even by the glass on the front of the container, must be a measure but the extent of the change in the field is not very large of strength – does for materials like glass, or air. It can be very large for this change if the materials like water and metals. ‘field’ has to pass through glass and What causes the change? It has to do with how the atoms metal – as the and molecules within a substance react to the applied field. Dutch-Metal (brass) If they have a strong response, then they affect the field experiment? strongly. Great first session! Glad you enjoyed it and glad you Very interesting practical examples which I will be able to take some can now use at home, so that’s objective no.1 experimental ideas home with you. already achieved. This week we will have more Interested in more examples regarding the examples about the propagation of propagation of EM wave e.g. light with light and the relationship between respect to atoms. light and atoms. Looking forward to next week. Me too What does Great question. It consists of – antimatter! Antimatter is ‘stuff’ antimatter but very strange stuff indeed. Each of the particles I told you consist of? about has an antiparticle – a kind of ‘sciency doppleganger’ – with opposite properties. So The antiparticle of an electron is called a positron, which has the same mass as an electron, but the opposite charge. The antiparticle of a proton is an antiproton, which has the same mass as a proton, but is negatively charged. The antiparticle of a neutron is an antiproton, which has the same mass as a neutron and no charge just like a neutron. The astonishing thing is that when an antiparticle meets its particle partner they annihilate each other leaving nothing but a burst of light! So how did we discover them? We first saw them in experiments using balloons to lift particle detectors high up into the atmosphere and saw that they arrived at the Earth from outer space. There are many mysteries about antimatter. Are they exactly the opposite of their matter particles? Why is world we know made of matter and not antimatter? Fascinating stuff! 13 You said… I loved the way you started with scale. When I think about the scale of the universe I feel terrified – but thank you for making me feel a little safer! Do you think there are other humans anywhere else but Earth? Michael said.. We often forget that ‘awe’ as in ‘awesome’ doesn’t mean ‘great’ it means terrifying! I think your reaction – terror! – is perfectly understandable. Give the size of the Earth – which seems so large to us as individuals – when we see the Earth in perspective to the rest of the Universe it is profoundly shocking. But that is just the way it is – and we need to keep on with our daily lives. I think there will be other life somewhere, but not humans. Humans are perfectly evolved to live on Earth – and we can never live anywhere else. Can we be sure These are the only types we have seen, And it raises the there is only +ve question: what is electrical charge? And since you ask, and –ve charges? electrical charge is a fundamental property of matter and we What is the can’t explain it in terms of anything else. distance between The distance between the nucleus and the orbiting electrons the nucleus and varies from one type of atom to another. the electrons. The nucleus is very tiny compared to the size of an atom. In units of picometres (1 pm = 10-12 m) a nucleus is typically 0.001 pm in diameter. In a hydrogen atom which has just one proton and one orbiting electron the average radius of the orbiting electron is 53 pm. In heavier atoms there are more protons in the nucleus and more orbiting electrons. The inner orbits are pulled in very tightly towards the nucleus but the outer orbits are usually a bit larger with a typical radius being ~ 100 pm. Is there a Well we don’t know of any definite minimum size, but there is minimum size a a length – called the Planck length after the scientist Max particle can Planck which marks a size at which we think our understanding reach or do they will definitely run out! This length is approximately 10-35 keep getting metres. It is difficult to conceive of this length but try this. smaller and The nucleus of an atom is around 10-15 metres in diameter, so smaller? the Planck length is smaller than a nucleus by a factor 1020 or 100 000 000 000 000 000 000 By comparison the nucleus is only a factor 1015 smaller than you are. So (in principle) all the complexity of life which exists between our everyday scale of life and the nucleus of atoms (this includes consciousness, brains, life, children, etc ) all of this could exist on a smaller scale between a nucleus and a Planck length. So to summarise, we can keep getting smaller for quite a long time yet! 14 You said… Really enjoyable, very clear visualisations. Question: Is this strong force constant? Very well explained. Good PowerPoint. Can you explain the interactions between molecules ever further? Michael said.. Thank you. Answer. I am not quite sure what you mean. You could mean ‘Has it changed in time since the big bang?’ We don’t think so. Or you could mean ‘Is it similar in strength between protons and protons, and protons and neutrons?’ It does vary slightly, but acts roughly equally between all protons and neutrons. Glad you liked the PowerPoint slides. Yes I can explain the interactions between molecules further. It’s difficult to answer such a general question but it is interesting to think about cases where we describe the interaction between molecules as chemical and when we describe them as physical. Think about two different types of atoms approaching each other so their outer ‘valence’ electrons come close. The key thing to think about is the strength of the electric field. ‘Noble gas atoms’ such as helium, neon and argon are almost perfectly spherical and have barely any electric field outside the regions where electrons orbit. This makes them chemically unreactive. All other atoms have relatively strong electric fields outside the atoms and are not perfectly spherical. As atoms approach each other, the outer (valence) electrons pick which atom has the strongest attraction. If the electrons make a move from one atom to another we call this interaction ‘chemical’. If the electrons stay with their original atom then we say there is no chemical reaction and call the interaction ‘physical’. Often the division is a bit blurred and many interactions are part-chemical and part-physical. But the key thing to remember is that it is all about electrical interactions! Does that make any sense? 15 You said… How do you change course in a vacuum. Michael said.. I think you are asking about how a rocket or satellite travelling through space can change course. Assuming that the rocket is not firing, the overall momentum of the rocket and all its contents are fixed. If it is not acted on by a force such as gravity, it will travel in a straight line with uniform speed – this is Newton’s first law of motion. In order to change direction (say to the right) some part of the rocket has move to the left. To do this a rocket shoots hot gas to the left. The momentum of an object is its mass × velocity. In order to change direction using the minimum amount of mass, the gas is made as hot as possible so that its molecules move as fast as possible. Thank you for a great first lesson. You are welcome. “what fun So many fun investigations to do with electricity. One thing I investigations have tried with mixed success has been making a Kelvin could someone do Water Dropper. If you a keen DIY-er it is quite do-able in an with afternoon electricity?..?” “.... or anything http://en.wikipedia.org/wiki/Kelvin_water_dropper to do with physics... that Other wise I have been thinking a lot lately about what makes wouldn’t result in things sticky… lots of experiments to try there! death?” When I tried to visualise one Mmmm. Well observed. The answer is that I think tenth of a millimetre I saw: so. We will talk more about diffraction this evening. Why am I not sure? Because I couldn’t photograph this effect. I tried with a microscope and a conventional camera and they don’t show the extra lines in between the upper and lower finger. I suspect this is a mixture of two effects, one Is this a diffraction effect? connected with diffraction and the other connected with some detail of human vision. I am a last minute substitute for a geeky I am glad you enjoyed yourself. father and would have said I was not that This is not the first time this has interested in science. happened! But I trust you and the I have thoroughly enjoyed this evening and geeky father will sort things out am looking forward to the rest of the course! amicably. It was an extremely That sounds excellent. I like the way you specify good session, I’ve learnt learning things you didn’t know before! At my age I a lot and many things take pleasure in learning things I didn’t know before I’ve never known but also in re-learning things I did know before – but before. have somehow placed to the back of my mind. 16 You said… Michael said.. I have learnt a lot from this week and It is a remarkable story and there learnt it in a fun and enjoyable way! It are many more fantastic stories really lets me think how electricity works about the key breakthroughs. and how people found it! Very entertaining and informative. Thank you. You are welcome Excellent! I am blushing again Where does Dark Well nobody knows! At the moment I think the basic Matter fit in the assumption is that ‘Dark Matter’ is a new kind of ‘stuff’ i.e. ‘Stuff’/’Not particles – of which we were previously unaware. I have Stuff’? heard people suggest it could be a kind of ‘not stuff’ i.e. a Great evening! field – of which we were previously unaware, but doesn’t seem Thanks. to be the vogue. As I explained somewhere else in these notes, we think ‘Dark Matter’ exists because of its effect on the motion of stars in galaxies. It could be that it doesn’t exist – but we just don’t understand something else about the motion of stars. The thing is – nobody knows! What does quark People don’t know what if anything makes up quarks. consist of? Quarks were discovered at the Stanford Linear Highly Accelerator (SLAC) in California – a straight version of entertaining and the LHC. The LHC smashes protons into other protons, intriguing – as but the SLAC smashed electrons into a target made of well as grasping liquid hydrogen and looked at the angles at which the my attention, it electrons emerged. really boosted Hydrogen is made of single protons, single electrons and and reinforce my lots of space, so most electrons go straight through the understanding. target. I’m looking We have never discovered any structure inside an forward to the electron – it behaves like a squishy ball of electric charge. next! So if protons were just point-like particles the scattering pattern of the electrons could be predicted. In fact people saw that occasionally electrons seemed to be scattered by tiny ‘hard’ point like-scatterers inside each proton. We have never discovered what makes up quarks but perhaps at some time we will. Thank you. It was great. You are welcome Best explanation of fields I Thanks you, what a lovely thing to say. have ever listened to, thanks. 17 You said… Michael said.. V. informative. Had a good I am glad you understand the links between understanding before but now chemistry and physics. Culturally, and in their appreciate the links between nomenclature, Physics and Chemistry are quite physics and chemistry better. distinct, but of course they are both describing Good P.P. the same physical reality. Excellent demo – engaged Glad your daughter enjoyed it and daughter and helped congratulations on her engagement. understanding. It’s amazing to think of myself Indeed. The complexity of what lies within us as a macro-Universe of billions and size of the Earth and the Universe is … and billions of particles and amazing and awe inspiring. fields. It is cool that I have electricity in me. Indeed. An atom is made out of If our culture collapses and you are the last protons, neutrons and person alive – pass this on to your children – it is electrons. an astonishing discovery. Good. I really enjoyed That level of complexity is exactly what I strive for. I it – complicated enough have struggled for years to get it right and it is not to be interesting, but there yet. In particular I find it very hard not to say not too complicated to extra things – qualifying each statement. In terms of be past me. Thank you! the oath taken in the witness stand, I promise to tell I really liked the the truth and nothing but the truth – but I can’t tell different way of the whole truth – otherwise you would be bored rigid! drawing the periodic Yes it is interesting to see that there are other ways to table, and the film was represent the periodicity. very interesting and eye-opening. Really brilliant Glad you enjoyed it. evening! I think you mean why did the electrons that got rubbed off Why do the my pullover onto the balloon stay there? electrical charges The answer is that they were trapped on the balloon that get moved to because the rubber of the balloon is an excellent make ions stay insulator. there? They don’t stay trapped on the balloon indefinitely because the rubber and the air are not perfect insulators. In particular there are lots of dust particles in the air and molecules of water that are strongly attracted to the charges on the surface on the balloon. These processes slowly reduce the concentration of charge on the balloon. 18 You said… Very interesting and helpful and well explained. I’ve never seen the other format of the Periodic Table, are the different groups the same just arranged differently? I enjoyed the experiments outside too. Thank you. When you put the slide up of the periodic table on the right hand side there was a second diagram. What was it? Michael said.. There are lots of other periodic tables. Try Wikipedia on the subject: http://en.wikipedia.org/wiki/Alternative_periodic_tables or just search Google with the search term “Alternative periodic tables”. These alternatives generally try to represent the fact that the periodicity in the elemental properties arises from the physical structure of electron orbits around atoms by having some kind of circular structure. The periodic table reflects the periodic physical structure of atoms with increasing numbers of protons and balancing electrons. Electrons orbit the nucleus in specific orbital patterns and some numbers of electrons can make a perfectly spherical closed ‘shell’ of charge. This is a configuration which has a very weak external electric field and so is chemically very un-reactive. Atoms with this configuration are o Helium (He) o Neon (Ne) o Argon (Ar) o These elements all have similar chemical properties Adding one proton and balancing electron makes an atom which has one electron orbiting a closed shell of charge. This one electron has a strong external electric field which makes these atoms chemically very reactive. These elements are o Helium + 1 proton and electron = lithium o Neon + 1 proton and electron = sodium o Argon + 1 proton and electron = potassium o These elements all have similar chemical properties 19 You said… Good jokes. I like the Tonight’s Drama thing. Need to be more prepared about the songs. Good presentation. Good experiments – but could not see it all clearly. Explanations were clear. I want to hear the song of elements. What is the chemical formulae of gold? Is it chloride and something? Michael said.. Jokes? Were there any jokes? Glad you liked the drama thing: that was a new slide – I don’t add slides easily – I prefer to take them away and try and say less. Yes, it’s normally the ‘live’ bits that go wrong. In this case the Flash player has changed how it handles files between the last presentation and now! Part of the problem was that at 4:30 a.m. the next morning I left to visit the European Space Agency in the Netherlands and I had spent the day preparing for two things instead of just one, and I missed my usual ‘click through’ before we started. What could you not see clearly? Please let us know and we will make sure you can see. You will hear the elements song this week! Gold is an element with the chemical symbol Au. It’s nucleus has 79 protons and 118 protons and it is orbited by 79 electrons. No it’s not a compound with Chlorine. I liked the video of zooming in and out from the Yes, that is great video. If man’s hand across the universe. you look on-line I think you I found the session fun and interesting. I have no can see how it was made current questions about this topic of electricity. and that is even more However, I do have a more life related question: amazing. What jobs are available at NPL? And how do I go Regarding work experience about applying for them? I am just finishing my and things you should just GCSEs so probably won’t be applying in the cold-call people: they can immediate future unless you do work experience or only say no! apprenticeships. 20 You said… Thanks Michael for making it so accessible and interesting and fun. Question: Nothing to do with electricity I suspect. Blue bubble bath makes the water blue buy the bubbles, however deep a handful are always white not blue. Surely lots of thin tiny, tiny layers should be blue? Nights of pondering over a pint at university and in decades since have never given me an answer. Can you? Michael said.. You are welome Answer: Well observed. The answer is connected with electricity because it is connected with light. It has to do with light ‘scattering’ – and hundreds of reflections. Think about glass or water which is mainly transparent. However most glass reflects about 4% of the light that falls upon it. Similarly water surfaces reflect about 4% of the light that falls on them. We can see this if the water surface is still – think about moonlight on the sea. The colour of the reflected light is the same as in the light source. Bubbles are made up of lots of surfaces and not very much liquid. So light which falls onto bubbles such as in a bubble bath undergoes lots At about age 6-7 (still at of reflections. Initially 4% is reflected leaving Infants School) my son’s 96% to travel onwards. At the next surface an question over tea was “So another 4% of that 96% is reflected. After a Mum, if you’re at the top of few hundred reflections the light ends up a mountain you’re nearer travelling in all kinds of directions, but has the sun so why is it pretty much the same spectrum as it did colder?” It took months of initially. So if you illuminated your bubbles with questions to everyone I white light, then bubbles will look white. knew till he got an The light does travel through a thin wall of the acceptable answer. His bubble which is made of liquid. In a ‘blue’ liquid, questions and interests the red light will be absorbed and the blue light haven’t stopped yet.... And transmitted. But because bubbles are mainly air he’s planning on Physics, and very little liquid, the colouring of the light is Chemistry, Maths, KT Anot very strong. Hence bubbles of all liquids – levels so that’s probably bubble bath or beer – are pretty much white. why. Hopefully the next six That is a great question and I am glad your son weeks will give him lots got to the answer eventually – and good luck more questions too! with his A levels! Feedback: Non-choc We had a biscuit emergency last week – a biscuits would be nice as delivery didn’t arrive and the Amey staff had to I’ve given up choc for Lent. run out and buy biscuits from Tesco! This week Guess I’ll wait till week 6! I expect more variety. Really interesting and mind boggling! Excellent! Thank you. You’re welcome 21