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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

what is electricity? part 3: capacitors, dielectrics and confusion

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an electrophorus, apparently

Canto: I’ve found a useful website on the history of the capacitor, which tells us that the term condenser was an early term for a capacitor, presumably because it accumulates charge, condensing it – like condensed milk?

Jacinta: Condensation in chemistry, or whatever, means transformation from a gas, or vapour, to a liquid. Remember they were thinking of an electrical fluid in the early days.

Canto: Well this excellent website on the early days tells me that the effect they were creating by rubbing  a glass globe is now called the triboelectric effect. And by the way it was Franklin who worked out that it was the glass that was creating the effect – nout to do with water, it seems.

Jacinta: Yes, it’s an everyday effect – you can get it just through combing your hair, or rubbing a plastic pen on your sleeve and then picking up bits of paper. I did it at school! I was very sciencey in them days.

Canto: Interestingly, there are lots of nice comments on this website, pointing out that the term for capacitor in a number of European languages is kondensator, or variants thereof. But we get yet another story here on early Leyden jars, which I’ll need to unpick:

It was realized also at Leyden University that it worked only if the glass container was held in your hand and not if it was supported by an insulating material. Today we realize that the alcohol or water in contact with the glass was acting as one plate of the capacitor and the hand was acting as the other while the glass was the dielectric. The high voltage source was the friction machine and the hand and body provided a ground.

Jacinta: So sometimes water was used as a ‘plate’ instead of the tin foil on the inner surface, and the hand was acting as the other plate. So, different versions of Leyden jars. And the dielectric? Yet another unexplained term.

Canto: Yeah, they just never simplify things enough for fuckwits like us. A dielectric is apparently an insulator. Or, as Wikipedia expands it, it’s ‘an electrical insulator that can be polarised by an applied electric field’. Now, I thought that an insulator was the opposite of a conductor, that it tends to be a bad conductor, something that’s difficult for a charge to pass through. Or is that a resistor? Anyway, I can see how dielectric, meaning two, has to do with polarisation, positive and negative, but it still remains vague. I just thought an insulator kind of protects people from getting electric shocks.

Jacinta: So, going back to Crump, here’s a quote:

Franklin succeeded in giving Leyden jars both positive and negative charges, and showed that the force itself was stored in the glass of the jar with the charge being proportional to its surface area.

I DO NOT UNDERSTAND THIS. I WANT TO UNDERSTAND. Does he mean positive and negative charges at the same time? Is that what a dielectric is? And when he says the force was stored in the glass, and the charge bore a mathematical relation to the surface area of the glass, does he mean a different thing by force and charge? And if the charge is proportional to the surface area of the glass, does that mean that if the surface area of the glass was equal to, say, the surface area of a glassy planet Earth, you’d get a more than respectable charge? And if our universe has a surface area?

Canto: The universe isn’t made of glass, I learned that from Dava Sobel’s The glass universe. Or not.

Jacinta: Okay, let me look up some common definitions before we go on.

dielectric is a material that transmits electricity without conducting. That’s to say, an insulator (BUT I DON’T UNDERSTAND WHAT THIS MEANS). Examples of dielectric materials include glass, ceramics, metallic oxides, plastics and dry air.

An insulator, electrically speaking, is a material in which electricity can’t flow freely. In such materials, electrons are tightly bound – though it’s all relative. They’re said to be resistive. So presumably there’s a connection between resistors and insulators. Most insulators are non-metals.

conductor is a material that allows a flow of electrrical charge, aka a current. Metals, such as copper wire, are commonly used as conductors.

Electric charge – and I think this is really the biggie – is a state or property of matter when a certain force from an electromagnetic field is applied to it. Or when it is within an electromagnetic field. But we won’t try to define an electromagnetic field until part 30 or so. An electric charge can be positive (carried by protons) or negative (electrons). This is not, of course, a full definition.

Triboelectricity is a charge of electricity gained by friction. The triboelectric effect can be varied and unpredictable, depending on the precise structure of the materials being rubbed together.

A capacitor, originally called a condenser, a term first coined by Volta, is… well, we posted a piece over four years ago called ‘What are capacitors?’ – but we’ve never thought about them since…

Canto: Yes, I’ve skimmed through that piece and I barely understand it. Let’s just say for now that a capacitor is a device for temporarily storing electricity, but that it differs from a battery somehow.

Jacinta: Okay, one more term used in Hackaday’s ‘History of the capacitor’ that needs explaining is hygroscopic. It says that soda glass, whatever that is, is hygroscopic. Franklin used soda glass in his experiments, apparently.

Canto: Google only tells me something about soda-lime glass, which I’m hoping is the same thing. It’s the most prevalent type of glass, composed of 70% silicon dioxide, or silica, 15% soda (sodium dioxide) and 9% lime (calcium oxide). The other 6% is made up of ‘other’. Hygroscopic materials attract water molecules from the surrounding environment, either by absorption or adsorption, but Wikipedia, which gives a large list of hygroscopic materials, makes no mention of glass or silicon as hygroscopic, though it does mention sodium salts.

Jacinta: So let’s move on with the history of these electrical discoveries, and maybe we’ll solve the problem of our own ignorance along the way. I note that potted histories of the battery, such as the one I’m about to quote from, don’t bother to distinguish between a battery and a capacitor:

Ben Franklin built an electric battery using glass window panes and thin lead plates. Using his “electric battery,” a term he coined himself, he showed how electricity could be stored in the glass and passed through it. Shouldn’t we call it the great-grand-dad of electric batteries?

So let’s not worry about it, though I suspect Yank jingoism is at play here. Let’s move on to Alessandro Volta.

Canto: And the continuous current battery. Volta’s first contribution to electricity was to improve on the electrophorus…

Jacinta: And here’s a great definition of the electrophorus, a device actually named by Volta:

An electrophorus or electrophore is a simple manual capacitive electrostatic generator used to produce electrostatic charge via the process of electrostatic induction.

Canto: Clear as mud. An electrophorus apparently consists of a dielectric plate…

Jacinta: Yeah, something that transmits electricity without conducting it.

Canto: Okay, let’s clear that up – perhaps. Dielectric materials don’t have free electrons for conducting electricity – they’re insulators. Electrons are, of course, electrically charged particles, and in dielectrics they’re tightly bonded to their nuclei. What does happen when an electric field or current is applied is that they become polarised. This raises the question of what polarisation actually is, and what it is about an electric field/current that causes this polarisation.

Jacinta: Not to mention whether there is a difference between an electric field and an electric current.

Canto: Okay, more work to be done. There are different types of polarisation. The polarisation of light, for example, is a complex story which we’ll have to deal with in another 50,000 part series. But here’s a general description from Britannica:

polarization, property of certain electromagnetic radiations in which the direction and magnitude of the vibrating electric field are related in a specified way.

So, just off the top of my head, an electric current seems to imply direction, whereas electric field not so much. On electric polarisation, ScienceDirect, which takes material from scientific papers, has this:

Electric polarization refers to the separation of center of positive charge and the center of negative charge in a material. The separation can be caused by a sufficiently high-electric field.

I think this means that dielectrics can be separated in terms of overall positive and negative charge in their individual atomic make-up, so that they can become magnetised, sort of? Because I think of magnetism in terms of polarity. They can become polarised, like magnets, while not being able to conduct an electric charge. Maybe.

Canto: We seem to have come a long way from capacitors.

Jacinta: We got lost on electrophoruses. An electrophorus consists of a dielectric plate..

Canto: Okay, here’s another definition, from Oxford Reference:

An early form of electrostatic generator. It consists of a flat dielectric plate and a metal plate with an insulated handle. The dielectric plate is charged by friction and the metal plate is placed on it and momentarily earthed, which leaves the metal plate with an induced charge of opposite polarity to that of the dielectric plate. The process can be repeated until all of the original charge has leaked away.

Jacinta: So this gives me a visible image, of sorts. The flat dielectric plate – and I assume a plate is something flat and thin – is polarised by friction, and a metal plate, that’s to say a conductor, is brought into contact with it and then momentarily earthed (I DON”T UNDERSTAND THIS), which leaves an induced charge of opposite polarity on this other plate )I DON”T UNDERSTAND THIS EITHER), and with repetition the original charge is leaked away (DITTO).

Canto: It seems every explanation needs further explanation, and we’re constantly changing electricity’s tail. And we’ve only just begun 🎵.

References

History of the Capacitor – The Pioneering Years

what are capacitors?

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

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

https://www.britannica.com/technology/soda-lime-glass

https://www.britannica.com/science/polarization-physics

https://www.oxfordreference.com/view/10.1093/oi/authority.20110803095746578

Written by stewart henderson

December 12, 2021 at 12:34 pm

What is electricity? part 1 – static electricity, mostly

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'Ben Franklin acquiring electricity', filched, methinks, from Reddit

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.quora.com/How-do-electrons-flow-in-a-circuit-Do-the-electrons-literally-move-or-is-there-just-a-transfer-of-energy-I-read-somewhere-that-the-direction-of-the-electrons-is-generally-unknown-Is-this-true

https://www.allaboutcircuits.com/textbook/direct-current/chpt-1/static-electricity/

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

https://www.quora.com/What-were-static-electricity-shocks-believe-to-be-during-antiquity-and-the-Middle-Ages

Thomas Crump, A brief history of science, 2001

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

Written by stewart henderson

November 28, 2021 at 8:52 pm

more on fuel cells and electrolysers

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Cross section of a PEMEL(polymer exchange membrane electrolyte?) stack comprising four cells, according to Science Direct

Jacinta: So continuing with Philip Russell’s simple video of a small hydrogen fuel cell (in the previous post), he explains that when the electrolysis process reverses itself, powering the fan, hydrogen is entering the cathode where it reacts with the palladium catalyst. The reaction with palladium is described as complex and weird, so he puts the matter off to a future video. In any case the hydrogen is split, producing electrons and hydrogen ions. Those electrons travel around the circuit which powers the fan, or a light bulb or some other electrical device, and the hydrogen ions travel through/across the PEM, where they react with the electrons in the circuit, and the oxygen, to produce water, which escapes from the anode side. 

Canto: So what they’re after in all this is the electrons, in sufficient abundance and in continuous supply to power whatever, without the use of carbon-based fuels. Frankly I’m not even sure how fossil fuels, hydrocarbons etc produce electricity, but hopefully I’ll learn something about this along the way.

Jacinta: You mean how does coal, oil or gas get transformed into high-energy electrons bumped along in a circuit? Yes, we have a lot to learn. 

Canto: And how do electrons in a wire make an air-conditioner work? But let’s stick with hydrogen for now. An older video, from 2012, from the excellent Fully Charged series, provides some other insights. I won’t go into too much detail with it, as the fuel cell described is very similar to Russell’s, but it does highlight some problems, at least from 2012. First, the interviewee, James Courtney from Birmingham University, uses the term proton-exchange membrane (PEM) rather than Russell’s PEM – a polymer exchange membrane. They mean the same thing, as the membrane is made of a polymer, and the key is that it’s an ‘electron insulator’, allowing protons to pass through. The polymer is usually nafion, a synthetic polymer created sixty years ago. It’s described as an ionomer for its ionic properties. But the most important thing I learned from Courtney is about the issue of platinum/palladium. It’s very very expensive, and its price is rising. Courtney – nine years ago – was experimenting with solid oxide electrolytes.

 Jacinta: From Wikipedia: 

solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte. Advantages of this class of fuel cells include high combined heat and power efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues.

Canto: An organisation called Bloom Energy, self-described as ‘a leader in the SOFC industry’, has a bit to say about the technology. So, again we have the negative anode and the positive cathode, and the electrolyte in between which undergoes ‘an electrochemical reaction’…

Jacinta: That’s when the miracle occurs.

Canto: Yes, and this produces an electrical current. So here’s something to think about re electrolytes: 

The electrolyte is an ion conductor that moves ions either from the fuel to the air or the air to the fuel to create electron flow. Electrolytes vary among fuel cell types, and depending on the electrolyte deployed, the fuel cells undergo slightly different electrochemical reactions, use different catalysts, run on different fuels, and achieve varying efficiencies.

Does that help?

Jacinta: Yes, it helps to complicate matters. 

Canto: So the Bloom Energy website reckons that SOFCs have the best potential for fuel cell technology, and promises they’ll bear fruit in the next six years – instead of the usual five. Here’s their diagram of an SOFC.

 

Note that they’re using natural gas (methane) in a process called methane reformation, also mentioned by James Courtney. So, not exactly a clean technology, but also, as the illustration mentions, no precious metals, corrosive acids or molten materials. 

Jacinta: But apparently this isn’t a hydrogen fuel cell. Barely a mention of hydrogen. 

Canto: Yes, the illustration presents oxygen ions reacting with ‘fuel in the fuel cell’ to produce electricity. The cleanness comes from the fact that there’s no combustion, making it more sustainable and of course more green than combustion-based tech. Apart from a partial reduction in greenhouse gases, this tech does away with the emission of harmful sulphur dioxide and nitrogen oxide. And their ‘Bloom box’ fuel cell packs can run on hydrogen, with net zero carbon emissions. They see their technology being well suited to distributed networks and mini-grids, which may provide the power supplies of the future.

Jacinta: We shall see – if we live long enough. Meanwhile let’s look at another video, featuring Dr Stephen Carr, of the H2 Centre, University of South Wales, on how a hydrogen fuel cell works. Eventually it’ll all come together.

Canto: And then fall apart again. This video is more recent than the previous two, but I’m not sure that there have been any new developments in the interval. So Dr Carr presents ‘a demonstration kit of a renewable hydrogen energy storage system’, in which the hydrogen is produced by solar power…

Jacinta: Another magical moment?

Canto: Well, apparently. Anyway, he represents the sun with a lamp – so I suppose it’s a demonstration, not the real thing. The lamp shines on a PV (photovoltaic) panel which produces electricity.

Jacinta: Grrr, they never explain that bit.

Canto: How do you produce annoyance? Bet you can’t explain that either. Anyway, the electricity runs through an electrolyser, which splits water into oxygen and hydrogen, which is stored for times when we can’t directly produce power from the sun. At such times we can run the hydrogen and oxygen through a fuel cell (which seems to operate oppositely to an electrolyser) to produce electrical power. As he says (and this is new) the photons from the lamp (in lieu of the sun) are converted by the panel into electrical energy or power (but I think those are two distinct things). This is of course referring to how solar energy/power works, which is an entirely different thing. We’ll leave that aside for now, along with the big heap of other things.

Jacinta: Yes let’s just focus on what Dr Carr says. The electrical power powers an electrolyser. The electrons are used to drive an electrochemical process which splits water into hydrogen and oxygen. On one side of this electrolyser the water is ‘split into hydrogen’ and on the other side it produces oxygen (magic happens). Then the hydrogen and oxygen can be stored until required, when we can somehow convert these elements into electricity. We can observe, as in the Philip Russell video, bubbles of hydrogen and oxygen forming on either side of the electrolyser, and being collected and stored. 

Canto: So we’re again not going to discover the detailed physics/chemistry of all this, but apparently we now have stored power. And this gets run backwards through the fuel cell. In the fuel cell, the released oxygen and hydrogen, in a reverse process to electrolysis (I think), produces pure, apparently drinkable water, and electricity. So the two gases are released from the electrolyser into the fuel cell, oxygen at one electrode, hydrogen at the other, and they’re combined and subjected to electrochemical processes (more magic), producing water and electricity sufficient in this tiny demo model to power a fan or small light. So far, precisely as enlightening as the Philip Russell video.

Jacinta: So next we’re taken to a big electrolyser, something like the new one at Tonsley, South Australia. It uses a stack of some 80 fuel cells to produce stacks of hydrogen. The electrolyser takes in about 50kw of power and produces about 1 kilogram of hydrogen per hour – which means very little to me. 

Canto: It’s good that they know this I suppose. So they have an electrolysis stack, and they feed in ‘pure de-ionised water’ – I bet we could do a whole post on that – and apply DC electric power – another post’s worth – which splits the water into hydrogen and oxygen.

Jacinta: When I think of AC and DC I think of Tesla v Edison. History is so much easier than science. I think we need to do a basic course in electricity. But continuing with Dr Carr, for what it’s worth to us, he says that ‘everything else in this unit is gas clean-up’. The hydrogen is ‘de-watered’ to make sure it’s completely dry, and it’s also de-oxygenated, in other words thoroughly purified. Then, for storage, it’s compressed to 200 bar, meaning 200x atmospheric pressure.

Canto: The bar, presumably for barometric pressure, is commonly used in Europe but not accepted by the US, centre of arseholedom with regard to weights and measures. 

Jacinta: The trouble is that ‘atmosphere’ for measures of atmospheric pressure, is highly contestable. Anyway, we’ll finish this off next time, for now I’ll just say that Elon Musk is still not much impressed with hydrogen technology, saying that hydrolysis is way too energy-intensive-expensive, that methane or propane etc extraction defeats the purpose, that hydrogen is too light to store easily, that it’s very volatile etc, but maybe it could work for aircraft in the future… So why is so much money being expended on it, in so many countries? Why is it suddenly such a big deal? That’s a ‘mystery’ we’ll have to investigate… 

References

https://www.sciencedirect.com/science/article/pii/S0360319919312145

The Hydrogen fuel cell explained, clean energy, by Philip Russell, youtube video

Hydrogen Fuel Cells | Fully Charged, youtube video

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

https://www.bloomenergy.com/blog/everything-you-need-to-know-about-solid-oxide-fuel-cells/

https://www.sciencedirect.com/science/article/pii/S1369702103003316

How does a hydrogen fuel cell work, with Dr Stephen Car, video

Elon Musk about Hydrogen Cars, video

Written by stewart henderson

July 7, 2021 at 9:27 pm

a hydrogen energy industry in South Australia?

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an artist’s impression of SA’s hydrogen power project

I recently received in the mail a brochure outlining SA Labor’s hydrogen energy jobs plan, ahead of the state election in March 2022. The conservatives are currently in power here. The plan involves building ‘a 200MW hydrogen fuelled power station to provide firming capacity in the South Australian Electricity Market’.

So, what does a ‘hydrogen fuelled power station’ entail, what is ‘firming capacity’ and what does 200MW mean?

A presumably USA site called energy.gov tells me this:

Hydrogen is a clean fuel that, when consumed in a fuel cell, produces only water. Hydrogen can be produced from a variety of domestic resources, such as natural gas, nuclear power, biomass, and renewable power like solar and wind. These qualities make it an attractive fuel option for transportation and electricity generation applications. It can be used in cars, in houses, for portable power, and in many more applications. Hydrogen is an energy carrier that can be used to store, move, and deliver energy produced from other sources.

This raises more questions than answers, for me. I can understand that hydrogen is a clean fuel – after all, it’s the major constituent, molecularly speaking, of water, which is pretty clean stuff. But what exactly is meant by ‘clean’ here? Do they mean ‘carbon neutral’, one of today’s buzz terms? Presumably so, and obviously hydrogen doesn’t contain carbon. Next question, what exactly is a fuel cell? Wikipedia explains:

A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requiring a continuous source of fuel and oxygen (usually from air) to sustain the chemical reaction, whereas in a battery the chemical energy usually comes from metals and their ions or oxides that are commonly already present in the battery, except in flow batteries. Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.

So the planned 200 megawatt power station will use the chemical energy of hydrogen, and oxygen as an oxidising agent, to produce electricity through a pair of redox reactions. Paraphrasing another website, the electricity is produced by combining hydrogen and oxygen atoms. This causes a reaction across an electrochemical cell, which produces water, electricity, and some heat. The same website tells me that, as of October 2020, there were 161 fuel cells operating in the US with, in total, 250 megawatts of capacity. The planned SA power station will have 200 megawatts, so does that make it a gigantic fuel cell, or a fuel cell collective? In any case, it sounds ambitious. The process of extracting the hydrogen is called electrolysis, and the devices used are called electrolysers, which will be powered by solar energy. Excess solar will no longer need to be switched off remotely during times of low demand.

There’s no doubt that the fortunes of hydrogen as a clean fuel are on the rise. It’s also being considered more and more as a storage system to provide firming capacity – to firm up supply that intermittent power sources – solar and wind – can’t always provide. The completed facility should be able to store 3600 tonnes of hydrogen, amounting to about two months of supply. There are export opportunities too, with all this excess supply. Japan and South Korea are two likely markets.

While it may seem like all this depends on Labor winning state government, the local libs are not entirely averse to the idea. It has already installed the nation’s largest hydrogen electrolyser (small, though, at 1.25 MW) at the Tonsley technology hub, and the SA Energy Minister has been talking up the idea of a hydrogen revolution. The $11.4 million electrolyser, a kind of proof of concept, extracts hydrogen gas from water at a rate of up to 480 kgs per day.

The difference between the libs and labor it seems is really about who pays for the infrastructure. Unsurprisingly, the libs are looking to the private sector, while Labor’s plans are for a government-owned facility, with the emphasis on jobs. Their brochure on the planned power station and ancillary developments is called the ‘hydrogen jobs plan’. According to SA’s Labor leader, Peter Malinauskas, up to 300 jobs will be created in constructing the hydrogen plant, at least 10,000 jobs will be ‘unlocked from the $20bn pipeline of renewable projects in South Australia’ (presumably not all hydrogen-related, but thrown in for good measure) and 900+ jobs will be created through development of a hydrogen export industry. He’s being a tad optimistic, needless to say.

But hydrogen really is in the air these days (well, sort of, in the form of water vapour). A recent New Scientist article, ‘The hydrogen games’, reports that Japan is hoping that its coming Olympic and Paralympic Games (which others are hoping will be cancelled) will be a showcase for its plan to become a ‘hydrogen society’ over the next few decades. And this plan is definitely good news for Australia.

Japan has pledged to achieve net-zero greenhouse gas emissions by 2050. However, this is likely impossible to achieve by solar or other established renewables. There just isn’t enough available areas for large scale solar or wind, in spite of floating solar plants on its lakes and offshore wind farms in planning. This is a problem for its hydrogen plans too, as it currently needs to produce the hydrogen from natural gas. It hopes that future technology will make green hydrogen from local renewables possible, but meanwhile it’s looking to overseas imports, notably from Australia, ‘which has ample sunshine, wind and empty space that make it perfect for producing this fuel’. Unfortunately we also have an ample supply of empty heads in our federal government, which might get in the way of this plan. And the Carbon Club, as exposed by Marian Wilkinson in her book of that name, continues to be as cashed-up and almost thuggishly influential as ever here. The success of the South Australian plan, Labor or Liberal, and the growing global interest in hydrogen as an energy source – France and Germany are also spending big on hydrogen – may be what will finally weaken the grip of the fossil fuel industry on a country seen by everyone else as potentially the best-placed to take financial advantage of the green resources economy.

References

Hydrogen Jobs Plan: powering new jobs & industry (South Australian Labor brochure)

https://www.energy.gov/eere/fuelcells/hydrogen-fuel-basics

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

https://www.eia.gov/energyexplained/hydrogen/use-of-hydrogen.php

‘The hydrogen games’, New Scientist No 3336 May 2021 pp18-19

Marian Wilkinson: The Carbon Club: How a network of influential climate sceptics, politicians and business leaders fought to control Australia’s climate policy, 2020

https://www.abc.net.au/news/2021-03-23/hydrogen-power-play-in-sa-as-labor-announces-gas-plant-project/100022842

Written by stewart henderson

June 24, 2021 at 7:49 pm

notes on the electrification of air travel

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stolen from NASA – hope I didn’t let the batt out of the bag

Air travel has become noticeably more popular over the past few decades – due largely to affordability. Even I can afford to catch a plane occasionally these days. And yet …

I realised something was out of kilter when I discovered that, in Europe, you can fly relatively cheaply from one major city to another by plane, whereas travelling by train costs more (sometimes much more) while being more efficient in terms of carbon emissions. So why is that, and what can be done about it?

Planes are generally more costly to run and, especially, to maintain than trains, and labour costs, too, are higher. Yet some of the larger airline companies are prepared to lose money on high-demand short-haul flights to maintain their profile, knowing they can gain on international flights. They can also be (or are) more flexible with their pricing, as this article points out, so that they can get bums on seats at suddenly slashed rates, filling their aircraft for each flight, unlike trains, which have basically operated under the same half-arsed system for over a century.

So, with the steady increase in domestic and international flights, and the lack of government oversight – e.g. taxation – of international airlines that transcend political borders, the carbon footprint of air flight (if that makes sense) is growing. A 2018 report on CO2 emissions stated that ‘using aviation industry values’ there was a 32% increase in aviation emissions in the previous five years. Which of course raises the question – how do we solve the problem of over-use of costly, environmentally-unfriendly jet fuel? The answer, of course, is electric propulsion. No? An electric motor is far simpler and easier to maintain than a jet engine (a turboprop engine has between 7000 and 10,000 moving parts). Energy costs are also cheaper, once a few problems are worked out – ahem.

The biggest problem, of course, is the battery. I’ve heard that AA batteries mightn’t be enough. Nor are the current generation of lithium-ion batteries, though innovation and research in this area is being driven by electric cars hoho. Clearly electric aircraft have to start small and short-haul, and they’re already doing so. I’ve written about this before, but it’s time for an update. Some of the companies involved include Pipistrel, Harbour Air and Eviation, but this is still extremely small-scale stuff as everybody waits for the battery boffins to perform the next miracle. Meanwhile, as with the motor vehicle industry, hybrids have been developed as a kind of stop-gap for larger capacity flights. Another company, Ampaire, has developed small hybrid aircraft with which it hopes to start daily operations in Hawaii in the near future. It’s also working in Norway, where they’re hoping to have all flights of 90 minutes or less to be be either fully electric or hybrid by 2040. I’m glad to hear that my birth country, Scotland is also investing in electric and hybrid planes for similar purposes. If these planes could be shown to be economically viable, then larger aeroplane companies will surely invest in them, as they tend to lose money on regional routes (small turbine engines being very inefficient). This could be the real game-changer, providing reason to invest in battery and other technology for longer electric flight. Changes in technology, combining standard aircraft design with helicopter design, are likely to make air flight more personalised in future, with less need to depend on airports. Of course this will come with regulatory and other issues, but it all makes for a more interesting future in the sky….

References

https://www.independent.co.uk/travel/news-and-advice/cheap-flights-ryanair-train-tickets-rail-price-fares-budget-plane-a8969291.html

Why don’t we have electric planes yet? CNBC video

Written by stewart henderson

December 29, 2019 at 4:14 pm