Charge on a battery’s terminals

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Recently when I was studying electrochemical cells, I was thinking about the fact that for a cell to drive current through an external circuit, the two electrodes must be at different potentials, and surely this means that there is a static charge on one or both of them. Otherwise how would they be at different potentials to begin with? I wanted to try and detect this charge.

I had come across this simple FET electroscope circuit some time back. It’s an amazing circuit where an LED is glowing by default, and turns off when a charged plastic scale is brought near the hanging gate of the FET. The electric field of the negative charge on the scale induces charges on the gate which turn the FET off. When you remove the charged scale from its vicinity, the LED comes back on.

The charge on the plastic scale is probably at a potential of thousands of volts, and the field is strong enough to make the FET turn off at a distance. But the charge on a battery’s terminal is obviously at a much smaller potential. So when I brought the negative terminal of a 9V battery near the gate of the FET nothing happened. But when I actually touched the negative terminal of the battery on the FET gate, the LED turned off and remained that way.

I think the LED stayed off because when I touched the gate of the FET with the negative terminal of the battery, some negative charge must have been transferred onto the gate, as opposed to the induced charges when the plastic scale was brought close. I could get the same result by rubbing the scale on the gate (not every time, because charge transfer from an insulator is not easy). If I now touch the gate with my finger the charge flows to me and the LED comes back on!

Unfortunately this doesn’t happen with single 1.5 V cells. I don’t understand why, but I read somewhere that the FET needs the field corresponding to around 7V or so of potential, to turn off. But the article linked to above says that it can detect potentials as small as one volt. But then I used a different FET to the one mentioned in the article. I need to understand FET’s better to make better sense of this.

According to what I’ve recently read in electrochemistry, it seems that even a single zinc plate dipped in acid, without a second electrode, develops an electrostatic charge, due to the different rate of oxidation of zinc atoms and reduction of hydrogen ions. It would have been amazing to be able to detect this charge.

Holding on to radical questions

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What is a radical question? Why do I get drawn to them? Why do they frustrate me?

I have a radical question when I believe that the way we generally do something is not smart, that there is a better way to do it. But we stick to the old way of doing things just because we have been doing it that way for a long time, and it’s convenient to just continue. And just keeping it going that way takes so much of our energy that we don’t look at things afresh.

This state of affairs pains me, since it pulls my energies in other directions rather than focusing them on work I believe in, work that I believe is best for myself and the people I’m working with. It’s not just the idea of this waste of time and energy, there’s a real pain and frustration coming from the organism within. I feel that pursuing the radical question has the potential to make my work more of play, at the same time making it more useful for the people I’m working with. There’s a romantic notion of a more wholesome, happier life associated with the radical question.

Wherever you are, there will be some constraints which you have to accept as existential. Obviously you are not going to change the whole world! When you put on paper what are the constraints you are willing to work under to pursue your radical question, and what is the test to decide if it’s useful to hold the radical question within the constraints you have accepted, I think the radical question has the potential to become real and woven into your work. If it’s unrealistic you can drop the radical question and live with the status quo or look for another situation with a different set of constraints to pursue your radical question.

And either way you would have probably learnt a lot in the process.

Simple programs for teaching integers and overflow

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While teaching unsigned and signed binary integers, I wrote these programs so that the students can run them and see overflow in action. There are four programs- addu, adds, subu and subs- for adding and subtracting 8-bit unsigned and signed integers. The numbers to be added are given as arguments when running the program. The result is printed on the screen and also saved in a file, which can be opened with a hex editor to see the result in binary format.

While the students where running the programs they obviously had questions about the the dot-slash. That was a good opportunity to tell them that all the commands they run, ls or cd or chmod or anything for that matter, are all executable files residing somewhere in the file system. I made them type which ls and find that ls is actually /bin/ls.

I pointed out the interesting fact that ls, which was somewhere else in the filesystem, could be run by just typing ls and not necessarily /bin/ls, while the addu program which was right here in this folder you needed to specify that it is in the current folder (they knew that dot stands for the current folder). Then I showed them how by adding the current directory to the PATH variable, you could run it by just typing addu, like any other command in the system.

Current without a ‘closed circuit’?

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It’s common knowledge that you need a ‘closed circuit’- an unbroken, continuous, conducting path- for an electric current to flow. If you are using a battery, this usually means an unbroken path from the positive terminal of the battery, through an LED (or whatever device you are running), all the way to the negative terminal of the battery.

But the closed loop between the terminals of the battery is strictly not necessary. What is important is that an electric current needs to flow through the LED, and for this all that is required is that the LED is connected between two points at different electrostatic potentials. The terminals of a battery contain static charges, and one could theoretically draw a small current for a small duration if we connected an LED between one terminal of the battery and a neutral object. The neutral object will act as a source or sink of electrons, depending on whether we are connecting it to the positive or negative terminal respectively. But for the chemical reactions in the battery to continue happening to provide a continuous current, the other terminal also needs to be operating (this is something that needs discussion, but I’ll do it in another post).

To test this out, I connected the positive lead of the LED to the positive terminal of a 9V battery, and held the negative lead with my fingers (myself being the neutral body). Obviously the LED didn’t light up. But then I connected the negative terminal of the battery to the earthing in an AC mains socket, so that it can act as a sink for electrons from the negative terminal of the battery. And the LED lit up! Not brightly, but that’s understandable, since my body has a large resistance.

Here’s a photograph of the LED glowing when I touch its negative terminal. The second picture shows the LED when it’s off, so that you can see the difference.

Teaching Computer Science Bottom-Up

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When I started teaching the new batch of Computer Applications students this year (class 9), I had it in my mind to do it bottom up, to try and give them a good sense of how computers actually work, how the 0’s and 1’s get so many things done. I wanted them to not only be able to write java programs in the prescribed IDE, but also have a good command over the machine, visualize what happens when they run a java program and easily learn other programming languages, work with microcontrollers and so on.

I started with teaching them how to use the GNU/Linux command line interface, to carry out the various tasks they normally do by clicking, dragging and dropping. Typing commands and making things happen turned out to be an exciting thing for them to learn. I had soon taught them to navigate the file system, copy and move files and folders, find out and change file permissions, open files using appropriate applications etc. It helped that I have just 4 students, all of whom are quite excited learning about computers and working on them.

Making them open files of different types with different applications gave me a context to introduce binary numbers and the different ways in which binary digit sequences can be interpreted. Usually it’s just stated that computers can work with only 0’s and 1’s, and that the 0’s and 1’s refer to different voltage levels etc. Then the focus turns to learning the binary number system, and the procedures to convert decimal numbers to binary and back, and some binary arithmetic.

But I saw the whole world of binary numbers in a new way, for the first time. What struck me was that computers interpret binary digit sequences in a variety of ways, not just as numbers. We want the computer to interpret binary numbers in several ways, as different kinds of data- text, numbers, images, audio- and instructions. I felt it would be exciting to try and pass on this understanding to the students.

I gave them a simple introduction to the binary number system, and then went on to making them edit text files and bitmap images using a hex editor. This gave them an idea of how the same set of bytes can be interpreted differently. As a project they even drew a 10×10 pixel image and typed in the hex code referring to the bitmap file format and saw the picture in an image viewer!

I then spent a few classes discussing the different kinds of numerical interpretations of binary numbers- unsigned integers, signed integers, fixed point numbers and floating point numbers. They also learnt about the problem of overflow because of the limited range of numbers. To illustrate overflow I wrote a few programs in C and made them run the executable from the terminal. That also gave me a context to talk to them about source code, compilation and the executable. (I was able to even explain to them the difference between proprietary and free software.) This was very useful, because the next interpretation of binary numbers I wanted to show them was that of instructions. I could easily tell them that the executable file contained bytes which the processor interprets as instructions.

And to actually show them this, I used the Hack CPU emulator developed by the authors of the book/course “The Elements of Computing Systems”. It uses a-simple-to-understand-yet-fully-functional hypothetical processor. I explained the architecture and instruction set to them, and even made them write an assembly program to add two numbers, to compare two numbers and to multiply two numbers by repeated addition. This made them learn important concepts like sequential execution of instructions, memory access, usage of registers, rudimentary arithmetic and logical operations, conditional and unconditional jumps- together they cover most of the concepts in elementary programming. And for each assembly program, I kept showing them the equivalent C program, and they were exclaiming how easy and intuitive the C programs are!

I’ll write in more detail about each of these later. But it’s been exciting for me to discover how children of 14 can learn computers at a level of detail that one would normally think is too advanced. And I strongly believe that this what’s-under-the-hood understanding will stand them in good stead whatever they learn in computers.

Rewriting ‘About me’

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I was rearranging my blog, and thought it was time to rewrite the ‘about me’ page- it turned out to be an interesting exercise. I thought I’d put it up as a post.

I or Me?

I wandered into teaching not with any clarity or passion for teaching, but confused and seeking a quiet place, and work where I could mess around with several interesting things. After two years and a little more of teaching science and computers, I find that I like teaching.

But larger questions in education remain. Having read radical thinkers in education like John Holt, I realize that the problems with schools and with education is a problem with the way our society has organised itself (right from the way families are organised, how parents have full time jobs that make it impossible for them to take care of their children, how the institution of childhood makes children inferior citizens with regards to things like how they spend their time and decisions that affect them- there is a cluster of issues) and it’s not something that can be solved in schools.

John Holt writes in Instead of Education, “During most of my teaching years, this is what I spent most of my time thinking about- immediate, concrete, practical matters. Not, how can I make schools better, or even help children learn better, but how can I help this child learn to spell this word or do this problem?” I try to keep myself grounded and live in my concrete reality, and not get lost and frustrated in the land of ideas and ideals. But I find that it’s difficult.

The radical questions can never go away, but I see that to pursue them would require stepping out of the designed environment of a school, and connecting with the world, which could happen one day if energies and momentum gather organically.

***

I’ve been writing this blog for over five years now. When I go through some of my old entries (some not so old), it strikes me how much I’ve changed over these years. I laugh at some of the things I’ve written. :) Sometimes you think you’re writing something profound and later when you read the same thing it looks like nonsense.

Of course I’ll continue writing nonsense, but I also plan to start writing about more concrete things, like my explorations in science, or some ideas that I tried out in class, or some computer program that I wrote, stuff like that which gives you a reassurance that you’re living in a concrete, physical world, and everything’s alright!

P.S. The title “I or Me?” is based the terms used in The User Illusion by Tor Norretranders to refer to the small part of ourselves that we become conscious of (I) and the whole organism that is Me.

Random Thoughts

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John Holt calls education “the ugly business of people-shaping”.

***

I’m convinced that it’s essential for one to have the freedom and leisure to mess around with whatever one is interested in or feels a fancy for at that moment. I don’t mean to say that one should not be asked to do anything. But whatever one has to do must be a real demand- a demand from somebody else that one has agreed to take up, or a demand that life throws at you. And having met the demand one must have the right to use one’s time as one wishes. Not only does it keep one in good spirits and enhance your creativity, but I think it is a fundamental right of any human being, of any age- as long as they are not harming somebody else.

***

The third year in teaching feels different. I feel like I have in my mind a richer map of the landscape of living and working in a school, just by having been in different kinds of situations with children, both inside and outside the classroom.

Keeping aside all the entanglements in the business of education given what our society is, I think children benefit from having adults around who are not very rigid in their thinking, who are doing something real that they enjoy, who can listen to children without having an educational motive all the time, and I think I partly fit that profile.

***

I probably can do a decent job here, but I don’t know if this work nourishes me. I do feel that being here has nourished me, whether it is partly due to the work with the children or whether it is completely independent of it but due to the environment, I do not know.

***

What nourishes me? What does this nourishment feel like? Is it more than just feeling good about one’s work? There seems to be a complex understanding of one’s work that you gain by going through a variety of experiences, and trying to make sense of them. I remember reading in “The User Illusion”, that stability is the foundation on which surprises can emerge, something truly creative can emerge. The science of complexity, I feel, gives an interesting way to make sense of our lives.

Stability can become linear and predictable and boring. And we try to make our lives more interesting by discarding stability and seeking out entirely new experiences which increases the possibilities in your life but also increases the disorder.

On the other hand, if one doesn’t stop asking questions and doesn’t start resigning oneself to things as they are just because one sticks with stability, I think the small and insignificant brush strokes which you enjoy making but think are meaningless can together make something interesting and unexpected. But you are not in conscious control of the emergence of complexity. You cannot foresee it.

You can only keep listening to your life and try to sense whether the linearity of stability is becoming boring, and if it is, try to study one’s brush strokes more closely instead of discarding the stability and seeking quick fulfillment in something else.

This is the insight which the science of complexity shows us. How is it different from the message of almost every religion? Probably the essence is the same.

But I find this insight neutral and devoid of any moral obligation or responsibility for working with oneself to reach a more enlightened state. All it says is that if you are bored with the linearity of your life, probably the more intelligent way to address this issue is to look at the little things you do and not yearn for a romantic wholesale change. The former allows complexity and meaning to emerge, while the latter will probably just increase disorder.

I don’t think anybody can understand this as an abstract concept and then try to live it. I see this insight when I try to make sense of the experiences I have already been through. I think everybody goes through a point in life when they feel bored with the linearity and yearn for romantic change. Sometimes they take the plunge, sometimes they persist with their earlier lives. In both cases, I think it is the subsequent investment of oneself in the small and insignificant brush strokes that lets complexity emerge from the linearity of stability.

***

Having been here for over two years now, I see that my brush strokes have allowed the emergence of some complexity and meaning. Probably it would have happened even if I had been working in an IT company or doing research. But taking a jump helped me move away from some of my mental blocks and look at life afresh.

But without having been through different experiences I don’t think I could have seen this. I think it is perfectly normal for any young person to reject and resist such ideas from elders as a simple advice of delaying gratification, coloured with a moral tinge. I think it comes only by being through various experiences and trying to make sense of them, and cannot be passed on through education, by sitting down together and talking. Even though elder people do it only wishing for the good of the youngsters.

It’s probably healthier for younger people to reject such advice and follow their instincts. One may or may not ‘do well’ in life, and nobody outside you can truly judge that. Either way you will be responding to real demands of life and possibly let a real understanding emerge, while accepting such an idea and limiting one’s own experiences can distort such understanding, I think.

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