Archive for the ‘electrons’ Category
advancing solar 2 – more on electrons, holes, dopants and electromagnetic fields
Jacinta: So in the last post we were joking about the horrors of physicists and engineers manipulating innocent electrons and forcing them to work for us, gratis. It comes to mind that there are people who are intelligently dubious about the manipulations of scientists – Bernard Beckett, in his 2007 book Falling for science, comes to mind, as does Yuval Noah Harari in Homo deus. ‘Scientism’ was used for a while as a pejorative, especially during the debates on the values of religion ‘versus’ science…
Canto: Yeah, but – I don’t want to dwell on this issue now, except to say that the critics of science are usually not very literate on the subject. So we were talking about dopants, which are impurities that can be added to the silicon crystal lattice to mess up its fine balance, so to speak. Boron is an example – it has three electrons ready for bonding, leaving a ‘hole’, a p-type space, and presumably a loose electron to carry the charge. And then there’s phosphorus, which has five such electrons – so one to spare after bonding, which they call an n-type situation. Positive charge carriers (p-type) and negative charge carriers (n-type) is how they describe it.
Jacinta: Right, so they layer these two types together: ‘The positive holes and negative electrons migrate towards each other’. The electrons will jump into the p-type and the holes jump into the n-type [they don’t explain how holes can jump]. This causes an imbalance of charge, because now the p-type side has more negative charges, and the n-type side has more positive charges’. This apparently creates an ‘electromagnetic valve’, which allows, or perhaps forces, electrons to pass through in one direction only.
Canto: This isn’t very clear to me, but let’s continue. Maybe you have to do it, and so see it working, to get a full grasp. So, a sufficiently energetic photon enters the p-type side (the boron-doped side) of the solar cell, knocking an electron loose to float within the material. It will either recombine with a hole, and fail to create a current, or it can enter the electromagnetic field – that valve thing between the p-types and n-types, also called a depletion layer for some reason. The effect, apparently, is that it accelerates the electron into the n-type side, which of course tends to lack p-type ‘holes’, but the electromagnetic field most cruelly prevents the electron from passing back to the p-type side.
Jacinta: Yes, it’s still a bit fuzzy, but on the n-type side some ‘holes’ are somehow transported across this electromagnetic field junction, where they recombine with electrons. so one side of this junction or valve becomes negatively charged, the other positive. This creates a ‘potential difference’, aka a voltage!
Canto: Explained neatly for us as ‘The difference in electric potential between two points, which is defined as the work needed per unit of charge to move a test charge between the two points’. Just saying.
Jacinta: So, as our video-maker tells us, we can then add ‘some mental contacts and an external load circuit’ and we have created a current, presumably, as the electrons will ‘pass along the circuit to recombine with the holes on the other side’. And that’s your solar cell, apparently. But I barely understand a word.
Canto: Well, doing and seeing, as I’ve said. But there’s problem with adding this metal to the upper surface as it blocks some of the light needed for the cell to function effectively. So, problems with solutions that create problems. So engineers keep working on new shapes and materials for optimisation. They’re trying to minimise the metal coverage and electron resistance in getting into the circuit. Topology optimisation is one subject of research, using computerised algorithms.
Jacinta: And it’s fascinating but hardly surprising that this sort of research is producing shapes for solar cells that resemble leaves – which after all are like little solar cells resulting from millions of years of evolution.
Canto: Hmmm, not like ours, plants don’t use the sun to make electricity. But this quote from the video is thought-provoking:
Vascular tissue on a leaf does not perform photosynthesis. It instead brings the water that is essential for photosynthesis to the leaf and extracts the useful products, serving a similar purpose as our electric contacts – so of course plants have developed the perfect shape to optimise the energy they can absorb from the sun… However, most solar cells use a simple grid shape, as it is cheap to manufacture.
Inevitably this means an efficiency loss, measured at around 8%. So, in conclusion, a current silicon solar cell has an efficiency, under lab testing, of around 20%. The drop to 18% shortly after operating has resulted in hundreds of scientific papers, and it seems to have to do with the use of boron, as the drop didn’t occur when boron was replaced with gallium. Something to do with a ‘boron oxygen defect’, so there’s been a lot of work done on trying to reduce the ‘concentration of oxygen impurities in the silicon wafers’, caused by the Czochralski process, the standard process for silicon wafer manufacturing. Almost all silicon solar cells are made this way. Recent research using a special imaging technique found that boron oxygen molecules converted to ‘shallow acceptors’ when exposed to light:
In essence they observed the defects transforming into little electron traps that acted as recombination sites, and thus reduced the time and probability of electrons entering the circuit to do work.
It’s something I can almost grasp. And with this knowledge, engineers, whose grasp is way firmer than mine, can find some kind of fix for the problem and get that efficiency up well beyond the 20% mark.
Jacinta: Well, this has indeed been a knowledge-expanding journey. Pour qu’une chose soit interessante, il suffit de la regarder longtemps. You mentioned the depletion layer, which caught my attention. It’s a central feature of semiconductor physics, also called depletion zone, depletion region, junction region and more. The depletion zone is so called because of the depletion of carriers in the region. Charge carriers presumably. Any rate, this region, and understanding it, is key to understanding the physics of semiconductors. The Wikipedia article on what they call the depletion region is a useful supplementary to our discussion. We might explore all this further, or not, depending on our own depletion levels…
References
The mystery flaw in solar panels (video)
https://en.wikipedia.org/wiki/Depletion_region
advancing solar, the photovoltaic effect, p-type semiconductors and the fiendishness of human manipulation
how to enslave electrons – human, all too human – stolen from E4U
Canto: Back to practical stuff for now (not that integral calculus isn’t practical), and the efficiencies in solar panels among other green technologies. Listening to podcasts such as those from SGU and New Scientist while walking the dog isn’t the best idea, what with doggy distractions and noise pollution from ICEs, so we’re going to take some of the following from another blog, Neurologica, which was also summarised on a recent SGU podcast.
Jacinta: Yes it’s all about improvements in solar panels, and the materials used in them, over the past couple of decades. We’re talking about improvements in lifespan and overall efficiency, not to mention cost to the consumer. Your standard silicon solar panels have improved efficiency since the mid 2000s from around 11% to around 28% – something like a 180% improvement. Is that good maths? Anyway, it’s the cheapest form of new energy and will become cheaper. And there’s also perovskite for different solar applications, and the possibility of quantum hi-tech approaches, using advanced AI technology to sort out the most promising. So the future is virtually impossible for we mere humans to predict.
Canto: Steven Novella, high priest of the SGU and author of the Neurologica post, suggests that with all the technological focus in this field today, who knows what may turn up – ‘researchers are doing amazing things with metamaterials’. He takes a close look at organic solar cells in particular, but these could possibly be combined with silicon and perovskite in the future. Organic solar cells are made from carbon-based polymers, essentially forms of plastic, which can be printed on various substrates. They’re potentially very cheap, though their life-span is not up to the silicon crystal level. However, their flexibility will suit applications other than rooftop solar – car roofs for example. They’re also more recyclable than silicon, which kind of solves the life-span problem. Their efficiency isn’t at the silicon level either, but that of course may change with further research. Scaling up production of these flexible organic solar materials has already begun.
Jacinta: So, I’ve mentioned perovskite, and I barely know what I’m talking about. So… some basic research tells me it’s a calcium titanium oxide mineral composed of calcium titanate (chemical formula CaTiO3), though any material with the ‘perovskite structure’ can be so called. It’s found in the earth’s mantle, in some chondritic meteorites, ejected limestone deposits and in various isolated locations such as the Urals, the Kola Peninsula in Russia, and such other far-flung places as Sweden and Arkansas. But I think the key is in the crystalline structure, which can be found in a variety of compounds.
Canto: Yes, worth watching perovskite developments in the future. I’m currently watching a video from Real Engineering called ‘the mystery flaw of solar panels’, which argues that this flaw has been analysed and solutions are being found. So, it starts with describing the problem – light-induced degradation, and explaining the photovoltaic effect:
The photovoltaic effect is the generation of voltage and electric current in a material upon exposure to light. It is a physical and chemical phenomenon.
Jacinta: Okay can we get clear again about the difference between voltage and current? I know that one is measured in volts and the other in amps but that explains nout.
Canto: Well, here’s one explanation – voltage, or emf, is the difference in electric potential between one point and another. Current is the rate of flow of an electric charge at any particular point. Check the references for more detail on that. Anyway we really are in the middle of a solar revolution, but the flaw in current solar panels is that newly manufactured solar cells are being tested at a little over 20% efficiency, that’s to say, 20% of the energy input from the sun is being converted into electric current. But within hours of operation the efficiency drops to 18% or so. That’s a 10% drop in generation, which becomes quite substantial on a large scale, with solar farms and such. So this is the problem of light-induced degradation, as mentioned. So, to quote the engineering video, ‘[the photovoltaic effect] is where photons of a particular threshold frequency, striking a material, can cause electrons to gain enough energy to free them from their atomic orbits and move freely in the material’. Semiconductors, which are sort of halfway between conductors and insulators, are the best materials for making this happen.
Jacinta: That’s strange, or counter-intuitive. Wouldn’t conductors be the best for getting electrons moving? Isn’t that why we use copper in electric wiring?
Canto: That’s a good question, which we might come back to. The first semiconducting material used, back in the 1880s, was (very expensive) selenium, which managed to create a continuous current with up to 1% efficiency. And so, silicon.
Jacinta: Which is essentially what we use, in inedible chip form, in all our electronic devices. Pretty versatile stuff. Will we always have enough of it?
Canto: Later. So when light hits this silicon crystal material, it can either be reflected, absorbed or neither – it may pass through without effect. Only absorption creates the photovoltaic effect. So, to improve efficiency we need to enhance absorption. Currently 30% of light is reflected from untreated silicon panels. If this wasn’t improved, maximum efficiency could only reach 70%. So we treat the panels with a layer of silicon monoxide reducing reflection to 10%. Add to that a layer of titanium dioxide, taking reflection to as low as 3%. A textured surface further enhances light absorption – for example light might be reflected sideways and hit another bump, where it’s absorbed. Very clever. But even absorbed light only has the potential to bring about the photovoltaic effect.
Jacinta: Yes, in order to create the effect, that is, to get electrons shifted, the photon has to be above a certain energy level, which is interesting, as photons aren’t considered to have mass, at least not when they’re at rest, but I’m not sure if photons ever rest… As the video says, ‘a photon’s energy is defined by multiplying Planck’s constant by its frequency’. That’s E = h.f, where h is Planck’s constant, which has been worked out by illustrious predecessors as 6.62607015 × 10−34 joule-seconds, according to the International System of Units (SI). And with silicon, the photons need an electromotive force of 1.1 electron volts to produce the photovoltaic effect, which can be converted, apparently, to a wavelength of 1,110 nanometres. That’s in the infrared, on the electromagnetic spectrum, near visible light. Any lower, in terms of energy (the lower the energy, the lower the frequency, the longer the wavelength, I believe), will just create heat and little light, a bit like my brain.
Canto: I couldn’t possibly comment on that, but the video goes on to explain that the solar energy we get from the sun, shown on a graph, is partially absorbed by our atmosphere before it reaches our panels. About 4% of the energy reaching us is in the ultraviolet, 44% is in the visible spectrum and 52% is in the infrared, surprisingly enough. Infrared red light has lower energy than visible light but it has a wider spectrum so the total energy emitted is greater. Now, silicon cannot use light above 1,110 nms in wavelength, meaning that some 19% of the sun’s energy can’t be used by our panels.
Jacinta: Yes, and another thing we’re supposed to note is that higher energy light doesn’t release more electrons, just higher energy electrons…
Canto: And presumably they’re talking about the electrons in the silicon structure?
Jacinta: Uhh, must be? So blue light – that’s at the short-wavelength end of the visible spectrum – blue light has about twice the energy of red light, ‘but the electrons that blue light releases simply lose their extra energy in the form of heat, producing no extra electricity. This energy loss results in about 33% of sunlight’s energy being lost.’ So add that 33% to the 19% lost at the long-wavelength end, that’s 52% of potential energy being lost. These are described as ‘spectrum losses’.
Canto: Which all sounds bad, but silicon, or its reaction with photons, has a threshold frequency that ‘balances these two frequency losses’. So, it captures enough of the low-energy wavelengths (the long wavelengths beyond the infra-red), while not losing too much efficiency due to heat. The heat problem can be serious, though, requiring active cooling in some climates, thus reducing efficiency in a vicious circle of sorts. Still, silicon is the best of threshold materials we have, presumably.
Jacinta: So, onto the next piece of physics, which is that there’s more to creating an electric current than knocking an electron free from its place in ye olde lattice, or whatever. For starters, ye olde electron just floats about like a lost lamb.
Canto: No use to anyone.
Jacinta: Yeah, it needs to be forced into doing work for us.
Canto: Because humans are arseholes who make slaves of everything that moves. Free the electrons!
Jacinta: You’ve got it. They need to be forced to work an electric circuit. And interestingly, the hole left when we’ve knocked an electron out of its happy home, that hole is also let loose to roam about like a lost thing. Free electrons, free holes, when they meet, they’re happy but the circuit is dead before it starts.
Canto: This sounds like a tragicomedy.
Jacinta: So we have to reduce the opportunities for electrons and holes to meet. Such is the cruelty of progress. For of course, we must needs use force, taking advantage of silicon’s unique properties. The most excellent crystal structure of the element is due to its having 4 electrons in its outer shell. So it bonds covalently with 4 other silicon atoms. And each of those bonds with 3 others and so on. A very stable balance. So the trick that we manipulative humans use to mess up this divine balance is to introduce impurities called dopants into the mix. If we add boron, which has 3 outer electrons, into the crystal lattice, this creates 3 covalent bonds with silicon, leaving – a hole!
Canto: How fiendishly clever!
Jacinta: It’s called a p-type trick, as it has this ‘positive’ hole just waiting for an electron to fill it. Sounds kind of sexy really.
Canto: Manipulation can be sexy in a perverse way. Stockholm syndrome for electrons?
Jacinta: Okay, there’s a lot more to this, but we’ve gone on long enough. I’ve had complaints that our blog posts are too long. Well, one complaint, because only one or two people read our stuff…
Canto: No matter – at least we’ve learned something. Let’s continue to rise above ourselves and grasp the world!
Jacinta: Okay, to be continued….
References
https://www.theskepticsguide.org/podcasts
https://news.mit.edu/2022/perovskites-solar-cells-explained-0715
The Mystery Flaw of Solar Panels (Real Engineering video)
https://byjus.com/physics/difference-between-voltage-and-current/
what is electricity? part 10 – it’s some kind of energy
je ne sais pas
Canto: We’ve done nine posts on electricity and it still seems to me like magic. I mean it’s some kind of energy produced by ionisation, which we’ve been able to harness into a continuous flow, which we call current. And the flow can alternate directionally or not, and there are advantages to each, apparently.
Jacinta: And energy is heat, or heat is energy, and can be used to do work, and a lot of work has been done on energy, and how it works – for example there’s a law of conservation of energy, though I’m not sure how that works.
Canto: Yes maybe if we dwell on that concept, something or other will become clearer. Apparently energy can’t be created or destroyed, only converted from one form to another. And there are many forms of energy – electrical, gravitational, mechanical, chemical, thermal, whatever.
Jacinta: Muscular, intellectual, sexual?
Canto: Nuclear energy, mass energy, kinetic energy, potential energy, dark energy, light energy…
Jacinta: Psychic energy… Anyway, it’s stuff that we use to do work, like proteinaceous foodstuff to provide us with the energy to get ourselves more proteinaceous foodstuff. But let’s not stray too far from electricity. Electricity from the get-go was seen as a force, as was gravity, which Newton famously explained mathematically with his inverse square law.
Canto: ‘Every object or entity attracts every other object or entity with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres’, but he of course didn’t know how much those objects, like ourselves, were made up of a ginormous number of particles or molecules, of all shapes and sizes and centres of mass.
Jacinta: But the inverse square law, in which a force dissipates with distance, captured the mathematical imagination of many scientists and explorers of the world’s forces over the following generations. Take, for example, magnetism. It seemed to reduce with distance. Could that reduction be expressed in an inverse square law? And what about heat? And of course electrical energy, our supposed topic?
Canto: Well, some quick net-research tells me that magnetism does indeed reduce with the square of distance, as does heat, all under the umbrella term that ‘intensity’ of any force, if you can call thermal energy a force, reduces in an inverse square ratio from the point source in any direction. As to why, I’m not sure if that’s a scientific question.
Jacinta: A Khan Academy essay tackles the question scientifically, pointing out that intuition sort of tells us that a force like, say magnetism, reduces with distance, as does the ‘force’ of a bonfire, and that these reductions with distance might all be connected, and therefore quantified in the same way. The key is in the way the force spreads out in straight lines in every direction from the source. That’s how it dissipates. When you’re close to the source it hasn’t had a chance to spread out.
Canto: So when you’re measuring the gravitational force upon you of the earth, you have to remember that attractive force is pulling you to the earth’s centre of mass. That attractive force is radiating out in all directions. So if you’re at a height that’s twice the distance between the earth’s surface and its centre of mass, the force is reduced by a particular mathematical formula which has to do with the surface of a sphere which is much larger than the earth’s sphere (though the earth isn’t quite a sphere), but can be mathematically related to that sphere quite precisely, or to a smaller or larger sphere. The surface of a sphere increases with the square of the radius.
Jacinta: Yes, and this inverse square law works for light intensity too, though it’s not intuitively obvious, perhaps. Or electromagnetic radiation, which I think is the technical term. And the keyword is radiation – it radiates out in every direction. Think of spheres again. But we need to focus on electricity. The question here is – how does the distance between two electrically charged objects affect the force of attraction or repulsion between them?
Canto: Well, we know that increasing the distance doesn’t increase the force. In fact we know – we observe – that increasing the distance decreases the force. And likely in a precise mathematical way.
Jacinta: Well thought. And here we’re talking about electrostatic forces. And evidence has shown, unsurprisingly, that the decreased or increased force is an inverse square relationship. To spell it out, double the distance between two electrostatically charged ‘points’ decreases the force (of attraction or repulsion) by two squared, or four. And so on. So distance really matters.
Canto: Double the distance and you reduce the force to a quarter of what it was. Triple the distance and you reduce it to a ninth.
Jacinta: This is Coulomb’s law for electrostatic force. Force is inversely proportional to the square of the distance – 
. Where F is the electric force, q are the two charges and r is the distance of separation. K is Coulomb’s constant.
Canto: Which needs explaining.
Jacinta: It’s a proportionality constant. This is where we have to understand something of the mathematics of variables and constants. So, Coulomb’s law was published by the brilliant Charles Augustin de Coulomb, who despite what you might think from his name, was no aristocrat and had to battle to get a decent education, in 1785. And as can be seen in his law, it features a constant similar to Newton’s gravitational constant.
Canto: So how is this constant worked out?
Jacinta: Well, think of the most famous equation in physics, E=mc2, which involves a constant, c, the speed of light in a vacuum. This speed can be measured in various ways. At first it was thought to be infinite, which is crazy but understandable. It would mean that that we were seeing the sun and stars as they actually are right now, which I’m sure is what every kid thinks. Descartes was one intellectual who favoured this view. It was ‘common sense’ after all. But a Danish astronomer, Ole Roemer, became the first person to calculate an actual value, when he recognised that there was a discrepancy between his calculation of the eclipse of Io, Jupiter’s innermost moon, and the actual eclipse as seen from earth. He theorised correctly that the discrepancy was due to the speed of light. Later the figure he arrived at was successively revised, by Christiaan Huygens among others, but Roemer was definitely on the right track…
Canto: Okay, I understand – and I understand that the calculation of the gravitational force exerted at the earth’s surface, about 9.8 metres per sec per sec, helps us to calculate the gravitational constant, I think. Anyway, Henry Cavendish was the first to come up with a pretty good approximation in 1798. But what about Coulomb’s constant?
Jacinta: Well I could state it – that’s to say, quote it from a science website – in SI units (the International System of units), but how that was arrived at precisely, I don’t know. It wasn’t worked out mathematically by Coulomb, I don’t think, but he worked out the inverse proportionality. There are explanations online, which invoke Gauss, Faraday, Lagrange and Maxwell, but the maths is way beyond me. Constants are tricky to state clearly because they invoke methods of measurements, and those measures are only human. For example the speed of light is measured in metres per second, but metres and seconds are actually human constructions for measuring stuff. What’s the measure of those measures? We have to use conventions.
Canto: Yes, this has gone on too long, and I feel my electric light is fading. I think we both need to do some mathematical training, or is it too late for us?
Jacinta: Well, I’m sure it’s all available online – the training. Brilliant.org might be a good start, or you could spend the rest of your life playing canasta – chess has been ruined by AI.
Canto: So many choices…
what is electricity? part 6: ohm’s law, electron flow and ac/dc, not explained
got it?
Canto: So we were getting into the behaviour of electrons in electrical field or currents, and the different ways electrons behave when voltage or electromotive force is applied to them, depending on the materials in which they’re embedded, whether that material is more or less conductive/resistant.
Jacinta: Which led to our light bulb moment. But we really need to look at electrons and their behaviour more closely, methinks.
Canto: I’ve noticed Quora questions such as ‘Why do electrons move against the electric field?’ and ‘Why do electrons experience force in direction opposite to electric field?’ Amongst other confusing things, responders note that there is simply a convention, created by Franklin. The convention being, I think, that electric fields/currents flow from positive to negative. This isn’t entirely clear to me, though I get the idea of conventional designations.
Jacinta: A number of responders point out, in different ways, that an electric current, say from a battery, flows from the positive terminal to the negative terminal. Electrons, being negatively charged, are repelled by the negative terminal and attracted to the positive terminal, due to the rule that like charges repel and opposite charges attract. So electrons flow in the opposite direction of the current/field. Which raises the question of why currents flow from positive to negative (presumably that’s just the convention).
Canto: So if the convention was turned around and we describe the flow as being from negative to positive, then we’d recognise the flow of electrons as going in that direction? I mean, which way do electrons flow really?
Jacinta: This might be a non-issue. A circuit attached to a voltage generator, such as a battery, sends the electrons in the direction of the current, which is arbitrarily designated as from the positive terminal to the negative one. Sounds like the electrons, negatively charged, are being pushed to the negative terminal, which would be expected to repel them, but that isn’t what’s happening. The electrons are just flowing in the direction of the current. Better to call the terminals A and B.
Canto: But if that was so, there’s an easy fix – we’d stop referring to those terminals as positive and negative. But I don’t think it is so. In one video I’ve watched, a battery is described as something which has two terminals, positively and negatively charged points, with a charge imbalance between them. The electrons are definitely described as being ‘pushed’ by the current from the negative point or terminal to the positive one, as you’d expect with opposite charges attracting. Though it also says that the flow of the charge is opposite to the flow of electrons, something to ponder. It also describes the negative point as a source, and the positive point as an attractor. The two-pronged electrical plugs use this system, one being the source, the other the attractor. And a ‘short circuit’ involves wires burning out because there is no resistance in the circuit – that’s to say, no appliances which work by applying resistance, which creates energy to run the appliance, as we saw with an incandescent bulb. Fuses act to prevent short circuits, cutting the current when the wire overheats.
Jacinta: Well, we seem to be learning something. This is better than a historical account it seems. But there are still so many problems. The ‘electricity explained’ video you’ve been describing says that the negative point is the source. So it’s saying negative to positive, simply ignoring the positive to negative convention. Perhaps we should too, but the video makes no mention of the convention, which confuses me.
Canto: Well, let’s push on. We’ll need to understand electrical fields, and of course the difference between ac and dc, and probably a host of other things, before we return to the historical discovery stuff, which of course is fascinating in its own quite different way.
Jacinta: Absolutely. And the relationship between electricity and magnetism, and Maxwell’s equations, haha. All without ever doing anything hands-on.
Canto: So I’m watching the apparently somewhat notorious recent Veritassium video on the subject, and I’ve learned in the first minute or so that a battery uses dc electricity whereas the grid connected to our homes uses ac. Though I knew that about the grid. Not that I know what it means exactly.
Jacinta: Yes, and he then says that in ac the electrons are just wiggling back and forth – as ‘alternating current’ suggests. But as mentioned earlier, I thought that was always the case – or, no, the electrons don’t flow, they just bump each other along, which obviously isn’t the same as ‘wiggling’. Each electron has moved, but only slightly. And I never thought of this in ac or dc terms.
Canto: So I’ve just watched the whole video, and I think I’ll pass on commenting at this stage. Obviously I don’t understand it all, nor do I understand the comments, many of them highly detailed.
Jacinta: Yes I think we should get our heads around the ac/dc stuff, and fields, then maybe get back to it.
Canto: This’ll probably take a lifetime, but we’ll start with direct current, dc. Your basic AA or AAA battery is a source of direct current. I’m looking at a typical AA 1.5 volt battery. It will provide 1.5 volts of, errr, voltage constantly in a circuit. Until it doesn’t. But also the circuit will have a resistance, measured in ohms, and we need to remember Ohm’s Law, from part 5, V (or E) = IR. That’s to say, the voltage is the current (I, in amps) multiplied by the resistance. I don’t know why that is, of course, but in any case a circuit connected by a certain voltage of battery will produce a particular current depending on the size of the resistance.
Jacinta: Like the dimensions of a pipe through which water flows. If you have one part of the pipe with a narrowed channel, that will effect the whole flow. The same with a resistor. And of course any wire will have resistance, depending on its conductivity. So why do we multiply the current by the resistance?
Canto: Ohm’s Law can be expressed as I = V/R. Here’s an elaboration of this:
This equation, i = v/r, tells us that the current, i, flowing through a circuit is directly proportional to the voltage, v, and inversely proportional to the resistance, r. In other words, if we increase the voltage, then the current will increase. But, if we increase the resistance, then the current will decrease.
I think it means that voltage will need to be increased to overcome the resistance, which reduces the current. It would be worthwhile to think of this in the brilliant.org way, to solve some simple problems. I’ve used study.com here, a site for engineers and such. Suppose you have a 10 volt battery connected to a light bulb with a resistance of 20 ohms. What is the current in the circuit?
Jacinta: So we have an equation with three variables. The current, in amps, is the voltage divided by the resistance, in this case 10/20, so the current should be 0.5 amps? Wow, I think I done some maths!
Canto: So if we double the voltage in this circuit, we double the current. Now, the great Khan, of Khan Academy fame, describes voltage as electric potential, as we’ve described before, or even energy potential. Think of a closed tap with potential energy. Open it, and you release kinetic energy in the flow. Current is measured as the flow of ‘electricity’, or electrical charge, per unit of time, I = Q/t. But then he confuses me with coulombs, which I’m not ready for. Q means charge (possibly measured in coulombs), and I’m not sure of its relation to V.
Jacinta: We’re equally confused. Let’s focus briefly on ac electricity. Alternating current involves this ‘wiggling’ of electrons mentioned before. Apparently electrons can be made to wiggle back and forth at particular rates, measured in cycles. Each cycle involves the electrons moving forward and then back to their starting points. In some grids, the electrons wiggle like this at 50 cycles/second, in others, e.g in the US, at 60 cycles/ second, or 60 hertz. How electrons can be made to do this I’m not sure – it presumably involves pulses of force? From both ends? Anyway, this form of electricity is apparently safer because it doesn’t heat up the wires so much. I can’t clearly see why though. But then you need transformers to connect the wires to your house, which uses direct current, I think. And as far as I know, a transformer is, like – here, a miracle happens.
Canto: So, more questions than answers here. What, exactly, is a transformer? How does it work? Why doesn’t ac electricity heat up the wires so much? How exactly is ac electricity created? Does every home need a transformer, or is it one transformer per street, or district….? it just goes on and on…
References
https://www.quora.com/Why-do-electrons-move-against-the-electric-field
What is electricity? – Electricity Explained – (1) , video from Into the Ordinary
Introduction to circuits and Ohm’s law | Circuits | Physics | Khan Academy
Alternating current, direct current & what is frequency? | Physics | Khan Academy
What is electricity? part 1 – static electricity, mostly
Canto: So it seems we’ve been here before but we’re back at the beginning again, because we’re still largely ignorant. And sadly, even if we finally get a handle on this complex phenomenon, we’ll be likely to forget it again through disuse, and then we’ll die.
Jacinta: So let me begin as naively as possible. Electricity is this energy source, or comes from this energy source, which travels through a wire by some kind of force that excites the electrons in the wire, which then oscillate and create an energy transfer along the wire, to a connector to a light bulb or a toaster, and when a switch connects the wire to the toaster it heats up your bread. But electricity doesn’t have to travel though a wire because I think lightning is electricity, but it needs a conducting material, which in the case of lightning is probably water vapour. I’ve heard somewhere that water is quite a good conductor of electricity.
Canto: Well, all that may or may not be true but what is voltage, what is current and why are certain materials conductors, and superconductors, electrically speaking, and what is an electric field? And I’ve heard that electrons really do flow in a wire, rather than just oscillating, though I’ve no idea what to make of that.
Jacinta: My next step is to look for experts, and to try to put their explanations into my own words, for ownership purposes. So I went to the ‘expert site’, Quora, and found quite a few contradictory or confusing responses, but assuming that the response that comes up first is some kind of popularly selected ‘best’ response, I’ll focus on Anthony Yeh’s answer. Oh by the way, the question is something like ‘what do electrons actually do in an electrical circuit?’ – though even that requires prior knowledge of what an electrical circuit actually is.
Canto: So let’s see if we can bed down the concept of an electrical circuit. So a website called ‘all about circuits’ gives us the basics, starting with static electricity. This was probably woman’s first discovery relating to the electrickery thing. Two different materials rubbed together – glass and silk, wax and wool – created this stickiness, this attraction to each other. And then it was noticed that, after the rubbing, the identical materials, such as two glass rods, exerted a force against each other. And another observation was that the wax, after rubbing with the wool, and the rod after rubbing with the silk, attracted each other.
Jacinta: Yes, this must’ve seemed quite bizarre to first discoverers. And they found that it worked as a sort of law. If the item was attracted by glass it would be repelled by wax – that’s to say, two rubbed wax cloths would always repel each other, as would the two rubbed glass rods. Which led to speculation about what was going on. The materials didn’t appear to be altered in any way. But they behaved differently after rubbing. Seemed like some invisible, quasi-magic force was in operation.
Canto: One of the earliest speculators that we know about was Charles du Fay (1698-1739). Note the dates – we’re really into the period inspired by Galileo, Newton and Huygens, the early days of theoretical and experimental physics. He separated the force involved into two, which he called vitreous and resinous. They were at first thought to be caused by invisible attractive and repulsive fluids. They later came to be known as positive and negative charges.
Jacinta: But when Benjamin Franklin (1706-90) came to experiment with what became known as electricity, it was still thought of as a fluid…
Canto: But hang on – this static electricity stuff must go back way earlier. Sparks fly, and you feel the energy on your skin when you remove, say, a piece of nylon clothing. And you see the sparks in the dark. I get it from metal door-handles quite regularly, and you can actually see it – it ain’t no fluid. Surely they noticed this way more than a couple of hundred years ago.
Jacinta: Okay let’s go back thousands of years, to Thales of Miletus, about 600 BCE. I’m using Quora again here. He noticed that rubbed amber was able to attract stuff, like leaves and other ground debris. Theophrastus, a student of Plato and Aristotle, who took over Aristotle’s Lyceum, also left some notes on this phenomenon, but this didn’t get any further than observation. William Gilbert (1544-1603), a much under-rated genius whom I read about in Thomas Crump’s A brief history of science, wrote a treatise, On the magnet, which compared the attractive, magnetic properties of lodestones with the properties of rubbed amber. He called this property ‘electric’, after elektron, the Greek word for amber. He also built the first electroscope, a simple needle that pivots toward an electrically charged body. Gilbert was able to distinguish between a magnet, which always remained a magnet, that’s to say, an attracter of metals, and an electrically charged material, which could easily lose its charge. So we’re now into the 17th century, and very far from understanding the phenomenon. The first electrical machine was constructed by Otto von Guericke (1602-86), another interesting polymath, in 1660. It was a rotating globe of sulphur, which attracted light material, creating sparks. Nothing new of course, but a useful public demonstration model.
Canto: So we’re now getting to a period when a few enlightened folks were set to wondering. And this was when they must’ve noted the phenomenon’s small-scale similarity to lightning.
Jacinta: Yes, and so experiments with lightning were undertaken in the eighteenth century, generally with disastrous results. The fact is, though Ben Franklin did do some experimentation with kites and lightning, he mainly focused on glass and amber rods. He noted, as before, that there were two different forces, or charges, attractive and repulsive. When a rubbed amber rod was brought toward another rubbed amber rod they repulsed each other. When the same amber rod was brought toward a glass rod, they were attracted. He considered there were two opposite aspects of the same fluid (for some reason investigators – at least some of them – was still thinking in terms of fluids). The identical aspects of the fluid repelled, while the opposite aspects attracted. He decided, apparently quite arbitrarily, to name one (glass) positive, the other (amber) negative. And we’ve been stuck with this designation ever since..
Canto: Yes, I’ve heard that it would have been much better to name them the other way round, but I’ve no idea why. And also, why is all this called static electricity? Obviously that name came later, but what does it mean? We hear people saying ‘I’m getting a lot of static’, which seems to mean some kind of interference with a signal, but I’ve no idea why it’s called that.
Jacinta: Oh shite, we’ll never get to the bottom of all this. Here’s a Wikipedia definition, which might help:
Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is named in contrast with current electricity, which flows through wires or other conductors and transmits energy
Canto: Okay, that helps. Static electricity ‘remains’ – it has to be discharged. So lightning is a discharge of static electricity?
Jacinta: I believe so, and that spark you get from the car doorhandle is a discharge of the static electricity built up in your body. Now let’s return to the online textbook ‘All about Circuits’. It points out that Ben Franklin did have a reason for his positive-negative designation. Here’s a quote:
Following Franklin’s speculation of the wool rubbing something off of the wax, the type of charge that was associated with rubbed wax became known as “negative” (because it was supposed to have a deficiency of fluid) while the type of charge associated with the rubbing wool became known as “positive” (because it was supposed to have an excess of fluid). Little did he know that his innocent conjecture would cause much confusion for students of electricity in the future!
Canto: Okay, I’m not sure whether this is a headfuck. When wax is rubbed with wool they attract each other. Franklin thought in terms of fluids, and he conjectured that, in the rubbing, the wool removed fluid from the wax – so wool had an excess of the fluid, and wax had a deficiency. The deficiency, which of course wasn’t really a deficiency, he termed ‘negative’ and the excess was ‘positive’. Sort of makes sense. Though why people since have felt this is the wrong way round, I don’t get at this stage.
Jacinta: So now we come to Charles-Augustin de Coulomb (1736-1806), and I suspect we’ll be dwelling on him for a while, because ‘All about circuits’ deals with him rather cursorily, methinks. It tells us that Coulomb experimented with electricity in the 1780s using a ‘torsional balance’ (wtf?) to measure the force generated between two electrically charged objects.
Canto: Exquisitely meaningless at this stage. Anyway, onward and downward…
References
https://www.allaboutcircuits.com/textbook/direct-current/chpt-1/static-electricity/
https://en.wikipedia.org/wiki/Charles_François_de_Cisternay_du_Fay
Thomas Crump, A brief history of science, 2001