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some more on hydrogen and fuel cells

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an electrolyser facility somewhere in the world, methinks

Canto: Our recent post on democracy and public broadcasting has made me turn to PBS, in order to be more democratic, and I watched a piece from their News Hour on clean hydrogen. Being always in need of scientific education, I’ve made this yet another starting point for my understanding of how hydrogen works as an energy source, what fuel cells are, and perhaps also about why so many people are so skeptical about its viability. 

Jacinta: Fuel cells are the essential components of hydrogen vehicles, just as batteries are for electric vehicles, and infernal combustion engines are for the evil vehicles clogging the roads of today, right?

Canto: Yes, and Jack Brouwer, of the National Fuel Cell Research Centre in California, claims that fuel cells can be designed to be just as fast as battery engine. Now according to the brief, illustrated explanation, diatomic hydrogen molecules enter the fuel cell (hydrogen occurs naturally in diatomic form, as does oxygen). As Miles O’Brien, the reporter, puts it: ‘A fuel cell generates electricity by relying on the natural attraction between hydrogen and oxygen molecules. Inside the cell, a membrane allows positive hydrogen particles [basically protons] to pass through to oxygen supplied from ambient air. The negative particles [electrons] are split off and sent on a detour, creating a flow of electrons – electricity to power the motor. After their work is done, all those particles reunite to make water, which is the only tailpipe emission on these vehicles.’  

Jacinta: He tells us that the oxygen is supplied by ambient air, but where does the hydrogen come from? No free hydrogen. That’s presumably where electrolysis comes in. Also, membranes allows protons to pass but not electrons? Shouldn’t that be the other way round? Electrons are much tinier than protons.  

Canto: Very smart. Maybe we’ll get to that. Brouwer talks of the benefits of fuel cells, saying ‘you can go farther’, whatever that means. Presumably, going farther with less fuel, or rather, you can have a lot of fuel on board, because hydrogen’s the lightest element in the universe. Clearly, it’s not so simple. O’Brien then takes us on a brief history of hydrogen fuel, starting with the conception back in 1839, and real-world application in the sixties for the Apollo missions. The Bush administration pledged a billion dollars for the development of hydrogen fuel cell cars in the 2000s, but – here’s the problem – they were producing hydrogen from methane, that infamous greenhouse gas. Ultimately the cars would be emission free and great for our cities and their currently dirty air, but the hydrogen production would be a problem unless they could find new clean methods. And that’s of course where electrolysis comes in – powered by green electricity. 

Jacinta: The splitting of water molecules, a process I still haven’t quite got my head around…. 

Canto: Well the PBS segment next focuses on the sectors in which, according to Brouwer, hydrogen fuel will make a difference, namely air transport and shipping. Rail and heavy vehicle transport too – where the lightness of hydrogen will make it the go-to fuel. It’s energy-dense but it must be compressed or liquefied for distribution. This makes the distribution element a lot more expensive than it is for petrol. So naturally Brouwer and others are looking at economies of scale – infrastructure. The more of these compressors you have, the more places you have them in, the cheaper it will all be, presumably. 

Jacinta: Right, as presumably happened with wind turbines and solar panels, and the more people working on them, the more people coming up with improvements… But how do they liquefy hydrogen?

Canto: Hmmm, time for some further research. You have to cool it to horribly low temps (lower than −253°C), and it’s horribly expensive. There was a bipartisan infrastructure bill passed recently which will fund the building of hydrogen distribution hubs around the USA through their Department of Energy. That’s where the action will be. The plan, according to mechanical engineer Keith Wipke of the National Renewable Energy Laboratory, is to do in ten years what it took solar and wind 3 or 4 decades to achieve. That is, to bring hydrogen production costs right down. He’s talking $1 per kilogram. 

Jacinta: Okay, remember that in 2032. 

Canto: Yeah, I won’t. They’re talking about improving every aspect of the process of course, including electrolysers, a big focus, as we’ve already reported. They’re connecting these electrolysers with renewable energy from wind and solar, and, in the bonobo-science world of caring and sharing, any new breakthroughs will quickly become globalised. 

Jacinta: Yeah, and Mr Pudding will win the Nobel Peace Prize…

References

Could hydrogen be the clean fuel of the future? (PBS News Hour video)

green hydrogen? it has its place, apparently

Written by stewart henderson

April 25, 2022 at 5:37 pm

green hydrogen? it has its place, apparently

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easy-peasy? don’t be guiled

Canto: So now that Labor has won government in South Australia it’ll be implementing its hydrogen plan pronto, I presume. But so many people seem iffy about hydrogen, I thought we might do another shallow dive on the topic.

Jacinta: Yes, we jointly wrote a piece last June on SA’s hydrogen plan (linked below), and a brief interview today with Andrew ‘Twiggy’ Forrest caught my attention – time to revisit and further our education on the subject.

Canto: Yes, a recent ABC article described Forrest’s ‘green hydrogen hub’ in Gladstone in central Queensland. He’s building the world’s largest electrolyser facility there. We’re talking gigawatts rather than megawatts. He expects – by which he means hopes – that the facility will have the capacity to produce 2 gigawatts (that’s 2000 megawatts) of electrolysers per annum, just for starters.

Jacinta: I’m not sure whether to trust Forrest’s hype, but I like his enthusiasm. He reckons he already has buyers for his electrolysers and that ‘the order list is growing rapidly’

Canto: Interesting – Forrest says that the lack of electrolysers has been a problem for a while, and apparently Australian researchers at the University of Wollongong, associated with a company called Hysata, have achieved a ‘giant leap for the electrolysis industry’, with its ‘capillary-fed electrolysis cells’, which have attained 95% efficiency, up from the previous 75%. This was published in the peer-reviewed journal Nature Communications, so it’s not just hot air.

Jacinta: Apparently electrolysers have been around for quite some time, with very few improvements, so this seems important. The researchers describe their approach thus:

The central challenge was to reduce the electrical resistance within the electrolysis cell. Much like a smart phone battery warming as it charges, resistance wasted energy in a regular cell as well as often requiring additional energy for cooling.

“What we did differently was just to start completely over and to think about it from a very high level,” Swiegers said. “Everyone else was looking at improving materials or an existing design.”

Canto: Reducing electrical resistance – that’s always the key to cheaper and more effective electricity, it seems to me. That was at the heart of the AC versus DC battle, and it’s what has made LED lighting such a vital development.

Jacinta: I still don’t understand LED lighting. Photons instead of electrons, yet still connected to an electric circuit driven by electrons in wires…

Canto: Anyway, returning to hydrogen, there’s a presumably new organisation called the Australian Hydrogen Council, whose website has a frequently asked questions section. The key thing about green hydrogen, or otherwise, is where the electricity comes from to produce electrolysis. To be green, obviously, it needs to be from solar or wind, or hydro. The FAQ section also mentions that the electricity can come from carbon capture and storage, resulting in ‘low to zero carbon emissions’.

Jacinta: Hmmm. We’ll have to do a shallow dive on carbon capture and storage soon. I know that ‘greenies’ are generally highly skeptical, but sometimes I feel a bit skeptical of greenies. Am I allowed to say that?

Canto: A generalised skepticism means looking critically at any scientific claims. But I’ve been thinking about electrolysis, particularly the electrolysis of water, which is key to this clean green hydrogen-producing process, presumably. It’s about ‘lysis’ – splitting, or separating – by means of an electrical current. But to paraphrase Woody Allen, ‘I’m two with science’. Or to put it another way, science is to me like a lover I’m passionate about but can never fully, or even partially, understand…

Jacinta: Well I’ve watched a wee citizen science video about doing electrolysis of water at home. You need, according to these guys, distilled  water, nice and pure, and ‘kosher’, non-iodised salt. Mix it together in a heat-resistant beaker, about nine parts water to one part salt, until the salt dissolves, and insert a couple of spoons attached to a nine volt battery into the mix. The salt increases the conductivity of the solution, as pure water isn’t conductive, much. You’ll need an acid, such as vinegar, to neutralise the alkaline solution that results from the experiment. That alkaline solution is essentially sodium hydroxide, NaOH, aka caustic soda or lye, which can cause burns, so home experimenters need to protect themselves accordingly. Then you insert the spoons, each connected to one of the two terminals of the battery, into the beaker. Bubbles of hydrogen and chlorine gas will form, as long as the two spoons are kept separate. Note that inhaling chlorine gas is a v bad idea, so, again, protection. And best to do the experiment outside. So what is happening here? Salt is an electrolyte, an ionically-bonded compound. The ions are what facilitates the transfer of electrical energy. So what we have in the solution are molecules of H, O, Na and Cl, the molecular bonds having been broken by the electrical current. In this home experiment, the hydrogen and chlorine gases escape into the air, but of course the hydrogen will be captured for energy use in the system being developed by Forrest and others.

Canto: Yes the salt water is used as an electrolyte, but different electrolysers will use different electrolytes. The US website energy.gov describes three types of electrolysers being used or considered at the commercial level – polymer electrolyte membrane (PEM), alkaline, and solid oxide. The problems with all these types is cost-effectiveness. For example the solid oxide membranes in that type of electrolyser need to operate at very high temperatures – between 700 and 800°C – to function effectively, though promising work is being done to lower the temperature. From what I can gather, the PEM electrolysers are showing the most promise. This uses a solid plastic electrolyte, and for what it’s worth I’ll quote something about how it works:

  • Water reacts at the anode to form oxygen and positively charged hydrogen ions (protons).
  • The electrons flow through an external circuit and the hydrogen ions selectively move across the PEM to the cathode.
  • At the cathode, hydrogen ions combine with electrons from the external circuit to form hydrogen gas.
  • Anode Reaction: 2H2O → O2 + 4H+ + 4e Cathode Reaction: 4H+ + 4e → 2H2

Jacinta: As you’ve said, the cost of electrolysers is a major barrier, and I’ve been unable to find out the type of electrolysers Forrest’s company (Green Energy Manufacturing) is going with. I did find out that Twiggy likes to be called Dr Forrest now, having completed a doctorate in Marine science recently. Also, there’s quite a lot of skepticism about his green hydrogen project.

Canto: Yeah, like there was with SA’s big battery… Stop Press –

The electrolysers produced at the GEM facility will partner FFI’s advanced manufacturing capabilities with cutting-edge Polymer Electrolysis Membrane (PEM) technology developed by NASDAQ-listed company Plug Power to deliver a high-purity, efficient and reliable end product.

That’s advertising blurb from the Queensland government, so we’ll have to wait and see. But getting back to the skepticism about hydrogen as an energy source – what gives? Well, according to Rosie Barnes, Australia’s engineering Wonderwoman, the process of creating hydrogen by electrolysis and then burnng it in a full cell is very energy-inefficient compared to direct or battery electrical energy. That’s three compared to one wind turbine, for example. Also hydrogen takes up a lot of space – remember those massive zeppelins?

Jacinta: Not personally.

Canto: Well, another problem with hydrogen is its flammability. The Hindenburg wasn’t the only hydrogen airship that went up in flames. They can replace hydrogen with helium apparently, but that presents another set of problems. In any case, it looks like hydrogen isn’t going to be the silver bullet for green energy, but it will surely be a part of the energy mix, and with technologies for storage and transport being developed and improved all the time, it’ll be interesting to see how and where green hydrogen finds its place.

Jacinta: Yes I’ll certainly be keeping an eye on the projects happening here in Australia, and how the likely change of government at the federal level makes a difference. My feeling is that they’re keeping mum about their energy plans until after the election, but maybe I’m being overly optimistic.

 

References

a hydrogen energy industry in South Australia?

https://www.abc.net.au/news/2022-02-28/andrew-forrest-begins-work-on-green-hydrogen-hub-in-gladstone/100865988

https://www.nature.com/articles/s41467-022-28953-x

The Sci Guys: Science at home – electrolysis of water (video)

https://www.energy.gov/eere/fuelcells/hydrogen-production-electrolysis

https://www.sciencedirect.com/science/article/pii/S2589299119300035

https://www.statedevelopment.qld.gov.au/news/people-projects-places/breaking-ground-how-aldoga-is-leading-queenslands-renewable-energy-charge

https://skepticalscience.com/hydrogen-fuel.html

Hydrogen and Helium in Rigid Airship Operations

 

Written by stewart henderson

April 18, 2022 at 5:57 pm

some stuff on super-grids and smart grids

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In a recent New Scientist article, ‘The rise of supergrids’, I learned that Australia is among 80 countries backing a project, or perhaps an idea for a project, launched at COP26 in Glasgow, called One Sun One World One Grid, ‘a plan to massively expand the reach of solar power by joining up the electricity grids of countries and even entire continents’. My first reaction was cynicism – Australia’s successive governments have never managed to come up with a credible policy to combat global warming or to develop renewable energy, but they love to save face by cheering on other countries’ initiatives, at no cost to themselves.

Our state government (South Australia) did invest in the construction of a giant lithium ion battery, the biggest of its kind at the time (2017), built by Tesla to firm up our sometimes dodgy electricity supply, and, to be fair, there’s been a lot of state investment here in wind and solar, but there’s been very little at the national level. 

At the global level, the Chinese thugocracy has been talking up the idea of a ‘global energy internet’ for some years – but let’s face it, the WEIRD world has good reason not to trust the CCP. Apparently China is a world leader in the manufacture and development of UHVDC (ultra-high voltage direct current) transmission lines, and is no doubt hoping to spread the algorithms of Chinese technological and political superiority through a globe-wrapped electrical belt-and-road. 

But back in the WEIRD world, it’s the EU that’s looking to spearhead the supergrid system. It already has the most developed international system for trading electricity, according to the Financial Review. And of course, we’re talking about renewable energy here, though an important ancillary effect would be trade connections within an increasingly global energy system. There’s also an interest, at least among some, in creating a transcontinental supergrid in the US. 

Renewable sources such as solar and wind tend to be generated in isolated, low-demand locations, so long-distance transmission is a major problem, especially when carried out across national boundaries. Currently the growth has been in local microgrids and battery storage, but there are arguments about meshing the small-scale with the large scale. One positive feature of a global energy network is that it might just have a uniting effect, regardless of economic considerations. 

But of course economics will be a major factor in enticing investment. Economists use an acronym, LCOE, the levelized cost of electricity, when analysing costs and benefits of an electrical grid system. This is a measure of the lifetime cost of a system divided by the energy it produces. The Lappeenranta University of Technology in Finland used this and other measures to analyse the ‘techno-economic benefits of a globally interconnected world’, and found that they would be fewer than those of a national and subnational grid system, which seems counter-intuitive to me. However the analysts did admit that a more holistic approach to the supergrid concept might be in order. In short, more research is needed. 

Another concept to consider is the smart grid, which generally starts small and local but can be built up over time and space. These grids are largely computerised, of course, which raises security concerns, but it would be hard to over-estimate the transformative nature of such energy systems.

Our current grid system was pretty well finalised in the mid-twentieth century. It was of course based on fossil fuels – coal, gas and oil – with some hydro. The first nuclear power plant – small in scale – commenced operations in the Soviet Union in 1954. With massive population growth and massive increases in energy demand (as well as a demand for reliability of services) more and more power plants were built, mostly based on fossil fuels. Over time, it was realised that there were particular periods of high and low demand, which led to using ‘peaking power generators’ that were often switched off. The cost of maintaining these generators was passed on to consumers in the form of increased tariffs. The use of ‘smart technology’ by individuals and companies to control usage was a more or less inevitable response. 

Moving into the 21st century, smart technology has led to something of a battle and an accommodation with energy providers. Moreover, combined with a growing concern about the fossil fuel industry and its contribution to global warming, and the rapid development of variable solar and wind power generation, some consumers have become increasingly interested in alternatives to ‘traditional’ grid systems, and large power stations, which can, in some regions, be rendered unnecessary for those with photovoltaics and battery storage. The potential for a more decentralised system of mini-grids for individual homes and neighbourhoods has become increasingly clear.   

Wikipedia’s article on smart grids, which I’m relying on, is impressively fulsome. It provides, inter alia, this definition of a smart grid from the European Union:

“A Smart Grid is an electricity network that can cost efficiently integrate the behaviour and actions of all users connected to it – generators, consumers and those that do both – in order to ensure economically efficient, sustainable power system with low losses and high levels of quality and security of supply and safety. A smart grid employs innovative products and services together with intelligent monitoring, control, communication, and self-healing technologies in order to:

  1. Better facilitate the connection and operation of generators of all sizes and technologies.
  2. Allow consumers to play a part in optimising the operation of the system.
  3. Provide consumers with greater information and options for how they use their supply.
  4. Significantly reduce the environmental impact of the whole electricity supply system.
  5. Maintain or even improve the existing high levels of system reliability, quality and security of supply.
  6. Maintain and improve the existing services efficiently.”

So, with the continued growth of innovative renewable energy technologies, for domestic and industrial use, and in particular with respect to transport (the development of vehicle-to-grid [V2G] systems), we’re going to have, I suspect, something of a technocratic divide between early adopters and those who are not so much traditionalists as confused about or overwhelmed by the pace of developments – remembering that most WEIRD countries have an increasingly ageing population. 

I’m speaking for myself here. Being not only somewhat long in the tooth but also dirt poor, I’m simply a bystander with respect to this stuff, but I hope to to get more integrated, smart and energetic about it over time. 

References

https://www.afr.com/companies/energy/the-future-of-power-is-transcontinental-submarine-supergrids-20210622-p5837a

Global supergrid vs. regional supergrids

https://en.wikipedia.org/wiki/Smart_grid

https://en.wikipedia.org/wiki/Vehicle-to-grid

Written by stewart henderson

March 15, 2022 at 7:33 pm

resetting the electrical agenda

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the all-electric la jamais contente, first car to break the 100 kph barrier, in 1899

In his book Clearing the air, Tim Smedley reminds us of the terrible errors we made in abandoning electric vehicles in the early 20th century. Smedley’s focus was on air pollution, and how the problem was exacerbated, and in fact largely caused, by emissions from car exhausts in increasingly car-dependent cities like Beijing, Delhi, Los Angeles and London. In the process he briefly mentioned the electric tram systems that were scrapped in so many cities worldwide in favour of the infernal combustion engine. It’s a story I’ve heard before of course, but it really is worth taking a deeper dive into the mess of mistakes we made back then, and the lessons we need to learn. 

A major lesson, unsurprisingly, is to be suspicious of vested interests. Today, the fossil fuel industry is still active in denying the facts about global warming and minimising the impact of air pollution on our health. Solar and wind power, and the rise of the EV industry – which, unfortunately, doesn’t exist in Australia – are still subject to ridiculous attacks by the heavily subsidised fossil fuel giants, though at least their employees don’t go around smashing wind turbines and solar panels. The website Car and Driver tells a ‘funny story’ about the very earliest days of EVs: 

… Robert Davidson of Aberdeen, built a prototype electric locomotive in 1837. A bigger, better version, demonstrated in 1841, could go 1.5 miles at 4 mph towing six tons. Then it needed new batteries. This impressive performance so alarmed railway workers (who saw it as a threat to their jobs tending steam engines) that they destroyed Davidson’s devil machine, which he’d named Galvani.

If only this achievement by Davidson, before the days of rechargeable batteries, had been greeted with more excitement and wonder. But by the time rechargeable batteries were introduced in the 1860s, steam locomotives were an established and indeed revolutionary form of transport. They began to be challenged, though, in the 1880s and 90s as battery technology, and other features such as lightweight construction materials and pneumatic tyres, started to make electric transport a more promising investment. What followed, of course, with the development of and continual improvements to the internal combustion engine in the 1870s and 80s, first using gas and then petrol – the 1870s into the 90s and beyond was a period of intense innovation for vehicular transport – was a serious and nasty battle for control of the future of private road transport. Electricity wasn’t widely available in the early twentieth century, but rich industrialists were able to create a network of filling stations, which, combined with the wider availability of cheap oil, and the mass production and marketing capabilities of industrialists like Henry Ford – who had earlier considered electric vehicles the best future option – made petrol-driven vehicles the eventual winner, in the short term. Of course, little thought was given in those days to fuel emissions. A US website describes a likely turning point: 

… it was Henry Ford’s mass-produced Model T that dealt a blow to the electric car. Introduced in 1908, the Model T made gasoline [petrol]-powered cars widely available and affordable. By 1912, the gasoline car cost only $650, while an electric roadster sold for $1,750. That same year, Charles Kettering introduced the electric starter, eliminating the need for the hand crank and giving rise to more gasoline-powered vehicle sales.

Electrically-powered vehicles quickly became ‘quaint’ and unfashionable, leading to to the trashing of electric trams worldwide. 

The high point of the internal combustion engine may not have arrived yet, as numbers continue to climb. Some appear to be addicted to the noise they make (I hear them roaring by nearly every night!). But surely their days are numbered. What shocks me, frankly, is how slow the public is to abandon them, when the fossil fuel industry is so clearly in retreat, and when EVs are becoming so ‘cool’. Of course conservative governments spend a fortune in subsidies to the fossil fuel industry –  Australia’s government  provided over $10 billion in the 2020-21 financial year, and the industry in its turn has given very generously to the government (over $1.5 million in FY2020, according to the Market Forces website).

But Australia is an outlier, with one of the worst climate policies in the WEIRD world. There will be a federal election here soon, and a change of government is very much on the cards, but the current labor opposition appears afraid to unveil a climate policy before the election. The move towards electrification of vehicles in many European countries, in China and elsewhere, will eventually have a knock-on effect here, but the immediate future doesn’t look promising. EV sales have risen markedly in the past twelve months, but from a very low base, with battery and hybrids rising to 1.95% of market share – still a paltry amount (compare Norway with 54% EVs in 2020). Interestingly, Japan is another WEIRD country that is lagging behind. China continues to be the world leader in terms of sheer numbers. 

The countries that will lead the field of course, will be those that invest in infrastructure for the transition. Our current government announced an infrastructure plan at the beginning of the year, but with little detail. There are issues, for example, about the type of charging infrastructure to fund, though fast-charging DC seems most likely.

In general, I’ve become pessimistic about Australians switching en masse to EVs over the next ten years or so – I’ve read too many ‘just around the corner’ articles with too little actual change in the past five years. But perhaps a new government with a solid, detailed plan will emerge in the near future, leading to a burst of new investment…. 

References

Tim Smedley, Clearing the air, 2019

https://www.caranddriver.com/features/g15378765/worth-the-watt-a-brief-history-of-the-electric-car-1830-to-present/

https://www.energy.gov/articles/history-electric-car

https://www.marketforces.org.au/politicaldonations2021/

 

Written by stewart henderson

February 27, 2022 at 1:07 pm

what is electricity? part 10 – it’s some kind of energy

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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 –     F = k \frac{q_1q_2}{r^2}. 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…

 

Written by stewart henderson

February 20, 2022 at 2:34 pm

what is electricity? part 8: turning DC current into AC, mostly

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Canto: So before we go into detail about turning direct current into alternating current, I want to know, in detail, why AC is better for our grid system. I’m still not clear about that.

Jacinta: It’s cheaper to generate and involves less energy loss over medium-long distances, apparently. This is because the voltage can be varied by means of transformers, which we’ll get to at some stage. Varying the voltage means, I think, that you can transmit the energy at high voltages via power lines, and then bring the voltage down via transformers for household use. This results in lower energy loss, but to understand this requires some mathematics.

Canto: Oh dear. And I’ve just been reading that AC is, strictly speaking, not more efficient than DC, but of course the argument and the technical detail is way beyond me.

Jacinta: Well let’s avoid that one. Or…maybe not. AC isn’t in any way intrinsically superior to DC, it depends on circs – and that stands for circuits as well as circumstances haha. But to explain this requires going into root mean square (RMS) values, which we will get to, but for now let’s focus on converting DC into AC. Here’s a quote from ‘all about circuits’:

If a machine is constructed to rotate a magnetic field around a set of stationary wire coils with the turning of a shaft, AC voltage will be produced across the wire coils as that shaft is rotated, in accordance with Faraday’s Law of electromagnetic induction. This is the basic operating principle of an AC generator, also known as an alternator

The links explain more about magnetic fields and electromagnetic induction, which we’ll eventually get to. Now we’ve already talked about rotating magnets to create a polarised field…

Canto: And when the magnet is at a particular angle in its rotation, no current flows – if ‘flow’ is the right word?

Jacinta: Yes. This same website has a neat illustration, and think of the sine curves.

Canto: Can you explain the wire coils? They’re what’s shown in the illustration, right, with the magnet somehow connected to them? And the load is anything that resists the current, creating energy to power a device?

Jacinta: Yes, electric coils, or electromagnetic coils, as I understand them, are integral to most electronic devices, and according to the ‘industrial quick search’ website, they ‘provide inductance in an electrical circuit, an electrical characteristic that opposes the flow of current’.

Canto: OMG, can you explain that explanation?

Jacinta: I can but try. You would think that resistance opposes the flow of current – like, to resist is to oppose, right? Well, it gets complicated, because magnetism is involved. We quoted earlier something about Faraday’s Law of electromagnetic induction, which will require much analysis to understand. The Oxford definition of inductance is ‘the property of an electric conductor or circuit that causes an electromotive force to be generated by a change in the current flowing’, if that helps.

Canto: Not really.

Jacinta: So… I believe… I mean I’ve read, that any flow of electric current creates a magnetic field…

Canto: How so? And what exactly is a magnetic field?

Jacinta: Well, it’s like a field of values, and it gets very mathematical, but the shape of the field is circular around the wire. There’s a rule of thumb about this, quite literally. It’s a right-hand rule…

Canto: I’m left-handed.

Jacinta: It shouldn’t be difficult to remember this. You set your right thumb in the direction of the current, and that means your fingers will curl in the direction of the magnetic field. So that’s direction. Strength, or magnitude, reduces as you move out from the wire, according to a precisely defined formula, B (the magnetic field) = μI/2πr. You’ll notice that the denominator here defines the circumference of a circle.

Canto: Yes, I think I get that – because it’s a circular field.

Jacinta: I got this from Khan Academy. I is the current, and μ, or mu (a Greek letter) stands for the permeability of the material, or substance, or medium, the wire is passing through (like air, for example). It all has something to do with Ampere’s Law. When the wire is passing through air, or a vacuum, mu becomes, or is treated as, the permeability of free space (μ.0), which is called a constant. So you can calculate, say, with a current of 3 amps, and a point 2 metres from the wire that the current is passing through, the magnitude and direction of the magnetic field. So you would have, in this wire passing through space, μ.0.3/2π.2, or μ.0.3/4π, which you can work out with a better calculator than we have, one that has all or many of the constants built in.

Canto: So easy. Wasn’t this supposed to be about alternating current?

Jacinta: Okay forget all that. Or don’t, but getting back to alternating current and how we create it, and how we switch from AC to DC or vice versa…

Canto: Let’s start, arbitrarily, with converting AC to DC.

Jacinta: Okay, so this involves the use of diodes. So, a diode conducts electricity in one direction only…. but, having had my head spun by the notion of diodes, and almost everything else electrical, I think we should start again, from the very beginning, and learn all about electrical circuits, in baby steps.

Canto: Maybe we should do it historically again, it’s more fun. People are generally more interesting than electrons.

Jacinta: Well, maybe we should do a bit of both. It’s true that we’re neither of us too good at the maths of all this but it’s pretty essential.

Canto: Okay, let’s return to the eighteenth century…

References

https://www.allaboutcircuits.com/textbook/direct-current/chpt-15/magnetic-fields-and-inductance/

Alternating Current vs Direct Current – Rms Voltage, Peak Current & Average Power of AC Circuits (video – the organic chemistry tutor)

 

Written by stewart henderson

January 16, 2022 at 6:19 pm

what is electricity? part 7 – alternating current explained, maybe

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Canto: So, alternating current is electrical current that alternates, or wobbles, or zig-zags, or cycles back and forth, at fifty or sixty cycles per second, aka hertz, but how and why?

Jacinta: Well, as Sabine would say, that’s what we’re going to talk about today. As always, when we look online for explanations, they tend to assume the reader or viewer has background knowledge by the bucketful. Here’s a typical example:

Many sources of electricity, most notably electromechanical generators, produce AC current with voltages that alternate in polarity, reversing between positive and negative over time. An alternator can also be used to purposely generate AC current.

It goes on to explain what an alternator is, but not very effectively for types like us.

Canto: We really need our own ‘For Dummies’ library.

Jacinta: The alternating current that’s used in our electrical grids has a neat sine wave form, undulating at precise intervals above and below a time line.

I’ll try to find out how we bring about alternating current, but first some points about its usefulness. As I think we mentioned before, AC is useful for transporting electrical energy, because it produces lower current at higher voltages (I DON’T REALLY UNDERSTAND THIS), so creating less resistance in the power lines, and so less energy lost as heat.

Canto: Some simple definitions, via Wikipedia et al, which we really need to keep reinforcing. Voltage is electric potential, or pressure, or tension. It’s usually analogised as water in a tank, or a boulder at the top of a mountain, ready to unleash its ‘tension’ by rolling downhill, and meeting resistance along the way, which makes things happen.

Jacinta: Did you know that there’s also three-phase AC power? OMG. But we talked in an earlier post about electrons only moving slightly, bumping the next electron along and so on. But, duh, I didn’t think that one through – that bumping action would be continuous, like people in a queue. You’d bump the person before and be bumped by the person behind, so the movement would be continuous, more or less, they’d all move from the positive to the negative. It’s what they call a chain reaction.

Canto: Interesting, but back to these analogies, I understood that a water tank has the potential to pour out water, and that a boulder has a potential to release kinetic energy down a mountain, but what is this potential energy that a battery has? It’s something called voltage, but that’s what I don’t understand. It’s the storage of a certain amount of electricity, like so much water. But I can visualise stored water. I can’t visualise stored electricity, or electric potential, or whatever.

Jacinta: Well, one day, understanding will dawn. Meanwhile, AC power, that’s when you get electrons to oscillate backwards and forwards, for example via a spinning magnet, which alternately repels and attracts electrons. It’s the movement of the electrons rather than their direction that creates the current.

Canto: Changing polarity. That’s what a spinning magnet will do (and maybe that’s what is meant by an alternator, or something like). And it will do it in an undulating rather than abrupt way. Very fast undulating – 50 cycles a second.

Jacinta: So I think we need to look at transformers, which are able to change the ac voltage, but not dc. Don’t ask why, at least not yet.

Canto: I’m looking at a vid which says that with AC the voltage varies, creating a sinusoidal function, as in the graphic above. But this explains nothing to me. Voltage is electric potential, but what really is that? I don’t want fucking analogies, I want the reality of it. How do you store this ‘electric potential’ in a battery, or whatever? And what really gets me about this and other videos are the comments – ‘great explanation’, ‘what a great teacher you are’, I’ve learned more from this than from months of study’ etc etc etc. And I’m thinking – am I a complete moron or what?

Jacinta: I feel your frustration, but we’ve promised to focus on AC, so just hold on to that question, which can be formulated as – How can a battery (or any other device) store electric potential for later use?

Canto: Which I suppose is something the same as – what is a battery (or an electric potential storage device)? How can you make one?

Jacinta: Anyway, a battery is used for DC energy, flowing from its positive to its negative terminal. That’s why, if you have batteries in series, like in the tube of my computer keyboard, they have to be in the right order, positive connected to negative terminals.

Canto: And if you have, say, three 1.5v batteries in series, that means you have 4.5v of ‘electric potential’?

Jacinta: Uhhh, let’s focus on AC. So, in Australia we typically have 230v household sources of AC electricity, oscillating, or changing polarity, at a frequency of 50 cycles/second, or 50 hertz. Imagine if you have a battery that’s spinning around so that the polarity is, well, spinning around too.

Canto: So if we have a 230v AC source in every home, is that like a gigantic spinning battery? I’d like to see that. Is that what an alternator is?

Jacinta: Well, if you look up ‘What’s an alternator’, you’ll generally find stuff about motor vehicles, but it’s definitely all about alternating current. And if you think polarity, you should think magnetism. So an alternator is essentially a magnet connected to an electric circuit, that changes polarity, usually by spinning, which creates a smooth alternation – back to the sine wave. We’re talking here about one-phase AC.

Canto: Yeah, we don’t presumably have alternators in our homes because it’s already AC in the wires, so it’s all AC?

Jacinta: Don’t confuse me. Running an electric current through a wire – usually copper – creates a magnetic field, and you can strengthen this magnetic field by coiling the wire. I’m not sure why, but this is essential electromagnetism, which we might understand one day. Anyway, this coil of wire is now an electromagnet, with its own polarity. Increasing the current induces a stronger magnetic field. If we run a magnet through the coil, we’ll create a stronger electric current, in DC form. Stop the magnet, and you stop that current. Reverse the magnet and you reverse the current. Push and pull the magnet in and out, and you create an AC current.

Canto: So that’s how sex can be electrifying – if it’s done fast enough?

Jacinta: Hmmm. The speed of the magnet’s movement does create a stronger current, as does the strength of the magnet.

Canto: Ahh, so it’s both the meat and the motion? Anyway, how to transform DC into AC – I’ve heard of a new device, or whatever – an inverter.

Jacinta: Ok, backing up, you’ve no doubt heard of the big battle between Edison and Tesla regarding AC and DC, back at the end of the 19th century. Well, Edison proved himself a bit of an arsehole during this battle, though the hero-worship of Tesla has since become a bit extreme. Since then, it’s been AC for big electrical networks worldwide, but DC is still used for car batteries and other smaller scale power. And, yes, an inverter is the device used to convert DC to AC.

Canto: Let me say that I do understand how AC works to create energy. It doesn’t matter if the movement is in one direction, or two, or a thousand. It’s the movement itself that creates the energy, which creates heat to boil your kettle or light your lamp.

Jacinta: Good, now there are rectifiers, which are a collection of diodes, which can convert AC to DC, but that’s for another post. An inverter comes in more than one type. Some use electromagnetic switches, reversing the flow abruptly, even brutally, with a pattern very different from our sine wave. More like castle crenellations. But electronic inverters use components such as capacitors and inductors – yes, they’ll be explained eventually – to smooth out the transitions. Transformers can also be used to change DC input voltage into a quite different AC voltage output, though of course, according to the law of conservation of energy, (first law of thermodynamics) you can’t get more power out of the system than you put in.

Canto: Changing the subject yet again, I was getting aerated about batteries, and I should’ve thought about them a bit more – I know that they get their electric potential from chemistry. I’ve been reading about Volta’s battery, made from zinc, silver and cloth or paper soaked in salty water. But that, and later improvements, and the mechanisms involved, are also for later posts.

Jacinta: Yes, a battery has an anode and a cathode and an electrolyte material separating them. A fun topic to explore more thoroughly. But we’re onto inverters. We need them to convert DC voltage providers, such as batteries and solar panels, into AC power for households. So batteries work to cause a current to flow, in say, a copper wire, and this creates a circuit between the cathode and the anode, heating up lamps and kettles along the way. But inverting the current, to create the sine wave pattern, or multiple such patterns, requires a magnet, coils and such. It’s complicated, so our next post will be horrible.

a pure sine wave inverter, apparently

References

What is Alternating Current (AC)? – Basic AC Theory – AC vs. DC (video)

Electric current (Khan Academy)

https://www.britannica.com/science/conservation-of-energy

https://www.explainthatstuff.com/how-inverters-work.html

 

Written by stewart henderson

January 11, 2022 at 5:35 pm

what is electricity? part 6: ohm’s law, electron flow and ac/dc, not explained

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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

https://study.com/academy/lesson/ohms-law-definition-relationship-between-voltage-current-resistance.html

Introduction to circuits and Ohm’s law | Circuits | Physics | Khan Academy

Alternating current, direct current & what is frequency? | Physics | Khan Academy

 

Written by stewart henderson

January 2, 2022 at 11:02 am

what is electricity? part 5: volts, amps, currents, resistance and final acceptance, almost

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A vintage Edison carbon filament light bulb – I stole this from Amazon.com, which every decent person should do

Jacinta: So the struggle continues, but I do feel we’re making progress, after having perused our previous posts. We’re perhaps being too hard on ourselves.

Canto: Yes, we’re geniuses actually, asking all the smart questions, not taking anything for granted. Anyway, we posted an image with part 4 of this series, which might help us to understand volts, watts and so forth. It tells us that volts are ‘a force that makes electricity move’, and that voltage measures ‘the potential difference between two points in a circuit’. I don’t fully understand this. It also tells us that watts are the product of voltage and current, P = VI, which we’ve already stated. I’m worried that we’ll be able to make calculations without really understanding the forces involved.

Jacinta: I suspect that our lack of hands-on experimental experience is hindering us. Even brilliant.org won’t really give us that.

Canto: This ‘potential difference’ concept is hard to grasp. Here’s another, apparently very different definition:

Voltage is the pressure from an electrical circuit’s power source that pushes charged electrons (current) through a conducting loop, enabling them to do work such as illuminating a light.

This takes us back to the safe ground of comparing electricity with water. But how does ‘pressure’ equate with ‘potential difference’?  Fluke.com goes on to introduce another headache. Voltage can come in two forms, alternating current (ac) and direct current (dc). We’re definitely not ready for that complication.

Jacinta: But further on this site gives an explanation of potential difference, again using the water analogy. Like water in a tank, voltage is more powerful (has more potential energy) the more water is stored, the bigger the tank etc. When the valve to the tank is opened, that’s like switching on the current, but there will always be resistance (ohms) in the dimensions of the valve or the pipe (the conductivity of the wire). And of course we’re talking of the ‘flow’ of electrons, but I seem to recall it’s more like the electrons are bumping against each other rapidly, a sort of knock-on effect. I may be wrong about that though.

Canto: Voltage is a measure of the potential capacity to do work – to push electrons into activity, whatever the detail of that activity is. I think that’s right. I don’t understand why it’s called potential difference, though, rather than potential energy, say.

Jacinta: Okay, I’ve just asked the internet that question. On Quora, someone with a PhD in theoretical physics says that it’s not actually potential energy, though somewhat related. There’s an equation, U = qV, in which U is potential energy, q is charge, and V is potential, or voltage.

Canto: Right, so voltage is very close to potential energy, because it’s the next letter in the alphabet.

Jacinta: Haha, your knowledge has always been too alphabetical. But apparently it has something to do with fields, and scalar and vector properties. Let’s not go there.

Canto: We might not be able to avoid it. Another Quora answer gives voltage the symbol E, apparently due to Ohm’s Law, I think because in Ohm’s day voltage was described as electromotive force.

E (or V) = IR (I being the current, R the resistance).

Jacinta: We haven’t really talked about electrons thus far, because we’ve been treating the subject historically and we’ve not got past the 18th century, but let’s jump to a modern understanding for a while. We now know that metals and other materials that can pass electrons from atom to atom easily are called conductors. Or rather, we now know that the reason metals are good at conducting electric currents is because of their atomic structure, where valence electrons, the electrons in the outer or valence shell, are loosely bound and can move or bounce from atom to atom within the atomic lattice. I think. Materials like glass and rubber are insulators for the opposite reason – tightly bound electrons.

Canto: So wires of good conducting material, such as copper, are insulated with rubber, to contain and direct the current. If these conducting materials don’t have a current connected to them, the valence electrons will move about randomly. Attaching an electric current to these materials pushes the electrons in a particular direction. Which raises the question – how does this happen? Where exactly does this force come from? 

Jacinta: It apparently comes from the voltage – but that sounds like magic. Of course, the source is a battery or some kind of electrical grid which is connected to households – a  sort of power storehouse. The source is a force.

Canto: Nice. But how does an electrical current move these electrons? For example, we know how water in a stream flows from the mountains to the sea. That’s the force of gravity. And I know how that works, sort of.

Jacinta: What is gravity? Will that be our next 50-part series?

Canto: In yet another intro to electricity I get the analogy of voltage and water pressure, which sort of explains how the force works, like water released from a tank, but it doesn’t explain what the force is. That’s the question – what actually is electricity.

Jacinta: But surely it actually is electrons flowing in a circuit, in a particular direction. Or in lightning. And here’s another definition – of a volt. It’s a joule per coulomb. A joule, in this definition, is a unit of energy or work, and a coulomb is a ‘group of flowing electrons’.

Canto: Fluids again. Anyway, the direction of the current seems to be described as positive to negative (though I’m wondering if the ac/dc distinction comes into play here), as in a small circuit connecting to those terminals in a battery. But why does a current ‘flow’ in this direction, assuming it does? Or are these just arbitrary designations, made up by Franklin?

Jacinta: And here comes another problem thrown up by one of these ‘explanations for dummies’. It distinguishes between a closed circuit, which enables ‘flow’, and an open circuit which prevents the electrons from flowing. I’ve never heard these terms before. Sounds counter-intuitive, but no explanation is given.

Canto: The meaning seems to be that you have to close the circuit to make the flow happen, between one battery terminal and the other for example. And that circuit might include light bulbs, heaters etc. Switching the bulb off means opening the circuit and stopping the flow, at least to that particular bulb. If it’s really a flow.

Jacinta: Well it does seem to be, according to this explainer. The claim is that electron flow is measured in coulombs or amps, because one coulomb equals one amp, though why they confuse us with two measures for the same thing is as yet a mystery. Apparently we can measure the flow of electrons as easily as we can measure the flow of water in a pipe. Which is surely bullshit. The explainer goes on to tell us that this electron flow is called current, and the unit of measure is an amp, or a coulomb.

Canto: Aren’t we going to find out about Monsieur Ampère and Monsieur Coulomb?

Jacinta: Not for a while. Our explainer tells us that one amp or coulomb equals the flow of 6242 plus fifteen more zeroes of electrons over a single point in the circuit in one second.

Canto: Hmmm. I’d hate to be the one counting that, especially within the time limit. Not so easy-peasy. But this is called a unit of electric charge, or electron charge, or elementary charge, and Britannica tells us this about it:

In 2018 the General Conference on Weights and Measures (CGPM) agreed that on May 20, 2019, the ampere would henceforth be defined such that the elementary charge would be equal to 1.602176634 × 10−19 coulomb. Earlier the ampere was defined as the constant current which, if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed one metre apart in a vacuum, would produce between these conductors a force equal to 2 × 10−7newton per metre of length.

Jacinta: Clarity at last! I need a drink. Anyway, our previous explainer seems to distinguish the group of electrons (a coulomb) from their passing one point in a second (an amp). I think. But let’s move on to something else to be confused about. Electrical currents don’t have to pass through wires of course but they do in our everyday electric circuits. And all these wires have a certain level of resistance.

Canto: Ohm, I think I know where you’re going with this.

Jacinta: The longer the wire, the more the resistance. The thicker the wire, the less the resistance. So in everyday circuits we have to find a compromise. And resistance is also temperature-dependent. Our circuits often incorporate resistors to deliberately restrict electron flow, which seems to be essential for lighting. Resistance within materials occurs when electrons collide with atoms, apparently.

Canto: And ‘conduction’ involves dodging atoms?

Jacinta: Well, it’s just electrons, not a game of Red Rover. Incandescent lights work by incorporating resistors, because the collisions release energy, which heats up the resistant tungsten wire in the bulb, producing light.

Canto: Ahh, that’s a real light bulb moment for me. And that’s not even a joke, though it also is.

Jacinta: Sounds like a great note to finish on. We’ll camp here for the night. For the road is long and winding, and I fear has no end….

References

https://www.fluke.com/en-au/learn/blog/electrical/what-is-voltage

https://www.quora.com/Why-is-voltage-sometimes-called-potential-Its-not-potential-energy-so-what-is-it-the-potential-of-The-electric-field

How electricity works – working principle (video – the engineering mindset)

https://www.britannica.com/science/ampere

https://www.qrg.northwestern.edu/projects/vss/docs/thermal/3-whats-a-resistor.html

Written by stewart henderson

December 23, 2021 at 10:58 pm

what is electricity? part 4: history, hysteria and a shameful sense of stupidity

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to be explored next time

Canto: So we’re still trying to explore various ‘electricity for dummies’ sites to comprehend the basics, but they all seem to be riddled with assumptions of knowledge we just don’t have, so we’ll keep on trying, as we must.

Jacinta: Yes, we’re still on basic electrostatics, but perhaps we should move on, and see if things somehow fall into place. Individuals noted that you could accumulate this energy, called charge, I think, in materials which didn’t actually conduct this charge, because they were insulators, in which electrons were trapped and couldn’t flow (though they knew nothing about electrons, they presumably thought the ‘fluid’ was kind of stuck, but was polarised. I presume, though, that they didn’t use the term ‘polarised’ either.

Canto: So when did they stop thinking of electricity as a fluid?

Jacinta: Well, a French guy called du Fay postulated that there were two fluids which somehow interacted to cause ‘electricity’. I’m writing this, but it doesn’t make any sense to me. Anyway this was back in 1733, and Franklin was still working under this view when he did his experiments in the 1740s, but he proposed an improvement – that there was only one fluid, which could somehow exist in excess or in its opposite – insufficiency, I suppose. And he called one ‘state’ positive and the other negative.

Canto: Just looking at the Wikipedia article on the fluid theory, which reminds me that in the 17th and early 18th century the idea of ‘ether’, this explain-all fluid or ‘stuff’ that permeated the atmosphere somehow, was predominant among the cognoscenti – or not-so-cognoscenti as it turned out.

Jacinta: Yes, and to answer your question, there’s no date for when they stopped thinking about ether or electrical fluid, the combined work of the likes of Coulomb, Ørsted and Ampère, and the gradual melding of theories of magnetism and electricity in the eighteenth and nineteenth centuries led to its fading away.

Canto: So to summarise where we’re at now, Franklin played around with Leyden jars, arranging them in sets to increase the stored static charge, and he called this a battery but it was really a capacitor.

Jacinta: Yes, and he set up a system of eleven panes of glass covered on each side by thin lead plates, a kind of ‘electrostatic’ battery, which accumulates and quickly discharges electric – what?

Canto: Electrical static? Certainly it wasn’t capable of creating electrical flow, which is what a battery does.

Jacinta: Flow implies a fluid doesn’t it?

Canto: Oh shit. Anyway, there were a lot of people experimenting with and reflecting on this powerful effect, or stuff, which was known to kill people if they weren’t careful. And they were starting to connect it with magnetism. For example, Franz Aepinus, a German intellectual who worked in Russia under Catherine the Great, published a treatise in 1759 with translates as An Attempt at a Theory of Electricity and Magnetism, which not only combined these forces for the first time but was the first attempt to treat the phenomena in mathematical terms. Henry Cavendish apparently worked on very similar lines in England in the 1770s, but his work wasn’t discovered until Maxwell published it a century later.

Jacinta: Yes, but what were these connections, and what was the mathematics?

Canto: Fuck knows. Who d’you think I am, Einshtein? I suppose we’re working towards Maxwell’s breakthrough work on electromagnetism, but whether we manage to get our heads around the mathematics of it all, that’s a question.

Jacinta: To which I know the answer.

Canto: So let’s look at Galvani, Volta and Coulomb. Galvani’s work with twitching dead frogs pioneered the field of bioelectricity – singing the body electric.

Jacinta: Brainwaves and shit. Neurotransmitters – we were electrical long before we knew it. Interestingly, Galvani’s wife Lucia was heavily involved in his experimental and scientific work. She was the daughter of one of Galvani’s teachers and was clearly a bright spark, but of course wasn’t fully credited until much later, and wouldn’t have been formally educated in those Talibanish days. She died of asthma in her mid-forties. I wish I’d met her.

Canto: So what exactly did they do?

Jacinta: Well they discovered, essentially, that the energy in muscular activity was electrical. We now recognise it as ionic flow. Fluids again. They also recognised that this energy was carried by the nerves. It was Alessandro Volta, a friend and sometime rival of the Galvanis, who coined the term galvanism in their honour – or rather in Luigi’s honour. Nowadays they’re considered pioneers in electrophysiology, the study of the electrical properties of living cells and tissues.

Canto: So now to Volta. He began to wonder about Galvani’s findings, suspecting that the metals used in Galvani’s experiments played a much more significant role in the activity. The Galvanis’ work had created the idea that electricity was a ‘living’ thing, and this of course has some truth to it, as living things have harnessed this force in many ways throughout their evolution, but Volta was also on the right track with his skepticism.

Jacinta: Volta was for decades a professor of experimental physics – which sounds so modern – at the University of Pavia. But he was also an experimenter in chemistry – all this in his early days when he did all his practical work in physics and chemistry. He was the first person to isolate and describe methane. But here’s a paragraph from Wikipedia we need to dwell on.

Volta also studied what we now call electrical capacitance, developing separate means to study both electrical potential (V) and charge (Q), and discovering that for a given object, they are proportional. This is called Volta’s Law of Capacitance, and for this work the unit of electrical potential has been named the volt.

Canto: Oh dear. I think we may need to do the Brilliant course on everyday electricity, or whatever it’s called. But, to begin – everyday light bulbs are designated as being 30 amps, 60 amps and so forth, and our domestic circuits apparently run on 240 volts. That latter is the electric potential and the amps are a measure of electrical output? Am I anywhere close?

Jacinta: I can’t pretend to know about that, but I was watching a video on neuroanatomy this morning…

Canto: As you do

Jacinta: And the lecturer informed us that the brain runs on only 20 watts. She was trying to impress her class with how energy-efficient the human brain is, but all I got from it was yet another electrical measure I need to get my head around.

Canto: Don’t forget ohms.

Jacinta: So let’s try to get these basics clear. Light bulbs are measured in watts, not amps, sorry. The HowStuffWorks website tells us that electricity is measured in voltage, current and resistance. Their symbols are V, I and R. They’re measured in volts, amps and ohms. So far, so very little. They use a neat analogy, especially as I’ve just done brilliant.org’s section on the science of toilets. Think of voltage as water pressure, current as flow rate, and resistance as the pipe system through which the water (and effluent etc) flows. Now, Ohm’s Law gives us a mathematical relationship between these three – I = V/R. That’s to say, the current is the voltage divided by the resistance.

Canto: So comparing this to water and plumbing, a hose is attached to a tank of water, near the bottom. The more water in the tank, the more pressure, the more water comes out of the hose, but the rate of flow depends on the dimensions of the hose, which provides resistance. Change the diameter of the hose and the outlet connected to the hose and you increase or reduce the resistance, which will have an inverse effect on the flow.

Jacinta: Now, to watts. This is, apparently, a measure of electrical power (P). It’s calculated by multiplying the voltage and the current (P = VI). Think of this again in watery terms. If you increase the water pressure (the ‘voltage’) while maintaining the ‘resistance’ aspects, you’ll produce more power. Or if you maintain the same pressure but reduce the resistance, you’ll also produce more power.

Canto: Right, so now we’re adding a bit of maths. Exhilarating. So using Ohm’s Law we can do some calculations. I’ll try to remember that watts are a measure of the energy a device uses. So, using the equation I = P/V we can calculate the current required for a certain power of light bulb with a particular voltage – but using the analogy of voltage as water pressure doesn’t really help me here. I’m not getting it. So let me quote:

In an electrical system, increasing either the current or the voltage will result in higher power. Let’s say you have a system with a 6-volt light bulb hooked up to a 6-volt battery. The power output of the light bulb is 100 watts. Using the equation I = P/V, we can calculate how much current in amps would be required to get 100 watts out of this 6-volt bulb.

You know that P = 100 W, and V = 6 V. So, you can rearrange the equation to solve for I and substitute in the numbers.

I = 100 W/6 V = 16.67 amps

I’m having no trouble with these calculations, but I’ve been thrown by the idea of a 6-volt light bulb. I thought they were measured in watts.

Jacinta: Okay, so now we’re moving away from all the historical stuff, which is more of our comfort zone, into the hard stuff about electrickery. Watts and Volts. Next time.

References

https://www.britannica.com/biography/Charles-Francois-de-Cisternay-Du-Fay

https://en.wikipedia.org/wiki/Fluid_theory_of_electricity

https://en.wikipedia.org/wiki/Leyden_jar

https://en.wikipedia.org/wiki/Franz_Aepinus

https://en.wikipedia.org/wiki/Henry_Cavendish

https://en.wikipedia.org/wiki/Luigi_Galvani

https://en.wikipedia.org/wiki/Lucia_Galeazzi_Galvani

https://science.howstuffworks.com/environmental/energy/question501.htm

https://byjus.com/physics/difference-between-watts-and-volts/

Written by stewart henderson

December 19, 2021 at 8:33 pm