Electrostatics in Middle-School – Part 3: Early Electrical Knowledge in the Classroom

Read the previous parts if you haven’t: Part 1 Part 2

In the previous article, I briefly introduced the major developments in the knowledge of electricity up to the first half of the 17th century. So, what lessons and activities for the classroom can be designed based on this?

I intend to describe one possible approach here. I leave it to the creativity and imagination of readers who may be teachers to think of better ways. I hope you’ll come back and share your ideas in the comments if you get inspired by this and come up with other ideas to try out!

From plastic ruler to amber

Every student would invariably have rubbed a plastic ruler on hair and observed tiny paper bits flying towards it. I would tell my students that people in ancient Greece had done the same thing with amber, as a starting point for the narrative. Although amber itself is a rare and expensive material and difficult to come by, some students would have read about it and would be eager to share with the class what they knew about it.

Is it magnetism?

It might seem like a trivial thing, but asking students whether they think that this attraction happens due to magnetism is a good way to get them warmed up for scientific inquiry. The students will be forced to articulate why the attracting power of the rubbed plastic ruler cannot be magnetism. And if you’re lucky, you may even have one student in class who asserts that it is magnetism and states her reasons — then it won’t be a trivial discussion any more!

Depending on how the debate unfolds, there may be opportunities to get the students to design simple experiments to check if a rubbed plastic ruler has any properties of a magnet.

  • Does a rubbed plastic ruler have poles? Are the paper bits attracted more strongly to the ends as in the case of iron pieces to a magnet?
  • Does the rubbed plastic ruler have any directionality? Does it align in the north-south direction if suspended by a thread?

Which other materials become attracting when rubbed?

The students can then repeat William Gilbert’s experiments to find out which materials around them get this attracting power when rubbed. I would get the students to make their own simple versorium by hanging a pencil from their desks with a thread. They would then pick up every substance they could find around them and check whether they can make the versorium rotate when rubbed. Some students might start exploring the question of whether the material used for rubbing matters.

Gilbert’s versorium
(Image: Public domain)

This activity is great fun, but it also quickly reveals the difficulties and limitations of scientific inquiry in the classroom. What the students will learn from the activity depends a lot on what materials they have with them to test with the versorium.

Ideally there would be several materials that are electrics and several that are non-electrics. However, this is not so easy in practice. Apart from most plastics like polythene, PVC, etc. there aren’t too many common materials that easily become charged on rubbing. In very dry weather, you can succeed in charging candle wax, a rubber eraser and sometimes paper — enough to detect with a versorium.

One question I was faced with was whether I should choose the set of materials I wanted the students to experiment with. I could make sure that there were different kinds of electrics and non-electrics in the set. But wasn’t that cheating? Wasn’t that in a way pre-determining what the students would “discover”? Could I even say that the students were “discovering” anything?

This is a complex question and I’ll share my thoughts on it in a later post. Here, it would suffice to say that in such situations, I’ve almost always tilted towards a pre-determined outcome — mostly due to my own personal discomfort with not knowing how a class will unfold!

Attraction and repulsion

One last experiment that can be done by the students based on this part of the story is on electrical repulsion. This can be demonstrated the first time, in case the students do not stumble upon this phenomenon on their own in the limited time they have.

It is actually the same experiment with the plastic ruler, but using small bits of aluminium foil instead of paper. With bits of aluminium foil, repulsion happens in a far more noticeable way when the pieces hit the ruler. Sometimes you can even get a foil piece to dance up and down between the ruler and the table!

Students can be asked to form their own hypotheses about why the aluminium foil pieces sometimes rebounded.

Electrostatics in Middle School – Part 2: Early Knowledge of Electricity

Read Part 1 if you haven’t.

Amber and Lodestone

Since antiquity, people have been fascinated and mystified by rare materials with special properties. Two such materials were amber — a fossilised resin from extinct pine-like trees — and lodestone — an iron-containing mineral that we now recognise as permanently magnetic.

The ancient Greek (4th century BCE) knew about the property of amber to attract light objects like feathers when rubbed. They also knew that lodestone could attract small bits of iron. Amber and lodestone were often mentioned in the same breath, because their powers to attract objects were strikingly similar.

An ant preserved in amber
Image: Anders L. Damgaard. CC-BY-SA

Jerome Cardan, a 16th century Italian mathematician and physician, was one of the first to make a clear distinction between the action of amber and lodestone. He noted that rubbed amber attracted any light object while lodestone attracted only objects made of iron. He also observed that the lodestone’s attraction was the strongest at its ends (poles) while amber seemed to have no such polarity.

Such distinctions between amber and lodestone remained scattered until the end of the 16th century. It was William Gilbert — Queen Elizabeth’s physician — who first studied electrical phenomena independently. His book De Magnete (“On the Magnet”) was published in 1600. The book was mostly about magnetism, but included Gilbert’s experiments on electricity. It is ironic that electricity was discussed only as a part of one chapter on magnetic attraction, yet it established the study of electricity as a separate branch of science.

William Gilbert demonstrating electrical experiments to Queen Elizabeth.
Image: Public Domain

Not just amber

Perhaps Gilbert’s greatest contribution to the study of electricity was his discovery that not just amber, but a large number of other substances too showed similar attractive powers when rubbed. His list included precious stones such as diamond, sapphire, carbuncle, opal and amethyst, artificial materials like glass, minerals like fluorspar from the mines, fossils like belemnites, sulfur and hard sealing wax.

Gilbert coined a new term for such materials which displayed the amber effect — he called them “electrics“.

The first electrical instrument

Gilbert also invented a handy little device to identify whether a substance was an electric or not. It consisted of a thin metal needle suspended such that it could rotate freely. If a rubbed electric was brought near one end, the needle promptly turned towards the electric. He called it the ‘versorium’ – Latin for ‘turn-about’.

Gilbert’s Versorium
Image: Public Domain

The versorium enabled Gilbert to detect even electrics with very weak attracting power, because the needle needed very little force to rotate on its support. Before the versorium was invented, an electric could be identified only if it directly attracted small objects, which needed a stronger force.

Do electrics repel too?

Thus far, all the studies on electricity only mentioned the power of attraction. In 1629, an Italian scholar named Niccolo Cabeo first reported that when a light object was attracted to an electric, often it rebounded to a distance of several inches after touching the electric. This seems to have been the first observation of electrical repulsion. Cabeo found this strange behaviour hard to explain, and the rebounding remained a mystery.

No significant progress in electrical research took place for almost another 100 years. Electricity continued to arouse the curiosity of scientists during this time, and several intriguing experiments were carried out. However, given that my primary purpose is to lay out a convenient narrative for teaching, I choose to skip them here.

***

In the next article, I will examine the lessons and classroom activities that can be designed based on the early discoveries discussed so far.

Reference

Duane Roller and Duane H. D. Roller. The Development of the Concept of Electric Charge: Electricity from the Greeks to Coulomb. Harvard Case Histories in Experimental Science – Volume 2

Sparks and Giggles: Electrostatics in Middle-School — Part 1 (Prelude)

Electrostatics and the school science curriculum

Electrostatics is a topic that sits awkwardly in the school science curriculum. In fact, it is hardly a topic in itself before it is introduced in all its mathematical glory in grade 11. Until then, students normally only encounter a handful of scattered electrostatic facts and phenomena without getting the opportunity to make meaningful connections.

As a student, I had carried out the ubiquitous experiment of rubbing a plastic ruler on my hair and seen little paper bits get attracted to it. I was told that this happened because the plastic ruler had become electrically charged. I was told that there were two kinds of charges, one was called positive and the other, negative. I was also told that the same kind of charges repelled each other and the opposite kinds attracted each other.

There seemed nothing unusual about all this, and I was happy to accept it as the truth. Many years later, I realised that perhaps it was the analogy with the easily observable magnetic poles that made it so easy to unquestioningly accept the existence of two kinds of electrical charges and their behaviour. (There is a fascinating historical connection here, which I will examine in an upcoming sequel.)

As an extension, the metal-leaf electroscope was touched upon, and so too the fact that lightning was a strong discharge of static electricity. That was all the electrostatics I learnt until grade 10, and I’m sure most others did, and continue to do today as well.

The neglect of electrostatics is not surprising at all when you look at the electrical devices around. Whether it is a lamp, a motor, a heater or a computer, almost all the devices we use work on electrical currents. There is a closed circuit involved, and there is electricity in motion. There are hardly any electrical devices in daily use where electrostatic charges build up and attract tiny bits of paper (old CRT-televisions being a notable exception, of course).

A blanket on fire and electrified children on chairs!

I grew up in the humid coastal state of Kerala. It was at the age of 22 that I moved to Pune for work. There, I first experienced a dry winter — when the relative humidity could fall as low as 20%. And one night I discovered that this had other ramifications apart from having to apply petroleum jelly to avoid cracked lips.

That winter, I was using a coarse woollen blanket provided by the school to cover myself while sleeping. One night, I woke up feeling cold. The blanket had slipped off my body. As I pulled the blanket back over me, I was dazzled by an intricate web of dim yellow sparkles emanating from the blanket. There was also a faint crackling sound.

Initially I thought I was dreaming and I pinched myself to check if I was. And no, the sparkling and crackling were real!

The next day, I spoke to a friend and colleague — also a science teacher — about what I saw. He explained to me that the extremely low humidity made it possible for electrostatic charges to accumulate to very high potentials, making such brilliant discharges possible.

I came to know from him that some children in the school had found innovative ways to have fun during dry weather. They would make one person sit on a plastic chair with her legs folded up. Another person would hit the back of the chair many times with a woollen sweater. Then, when you touch the person sitting on the chair, you get a strong shock that makes you jump!

It all started with electrostatics

All this piqued my curiosity immensely and I was lucky to find two indispensable sources to learn more about electrostatic phenomena. One was the BBC Four documentary series – Shock and Awe: The Story of Electricity hosted by Jim Al-Khalili, and the other was the Harvard Case History on the development of the concept of electric charge.

And what I learned from these sources completely turned the tables on what I thought I knew about electricity. For the first 200 years or so of its development (roughly 1600-1800), ‘electricity’ meant electrostatic phenomena. There were no batteries, no motors, no devices that you would recognise today as ‘electrical’. And an awful lot was discovered about electricity during this time.

This made me wonder if it was possible to approach the teaching of electricity in school from an entirely different angle. One that paralleled the historical development of ideas, and drew on those stories of discovery.

This was 2011, I was teaching chemistry to grades 9 and 10, and I wasn’t able to actually try this out. In 2013, I left teaching to explore other areas of work. However, I did return to teaching in 2016 and this time I had grade 6 science to teach. Exactly the age group I wanted to explore electrostatics with.

In the coming posts, I intend to document my attempt at teaching electrostatics using a historical approach to eager 11-year olds.

A Medical Doctor’s Sabbatical to Do Science Experiments

A forgotten name in science

Key contributions to scientific knowledge are almost always intertwined with the names of the scientist(s) who made those contributions. A glaring exception exists in the case of one of the most fundamental discoveries of all in the life sciences – photosynthesis.

Jan Ingen-Housz (1730-1799) was a Dutch physician who, at some points in his career served as the family doctor to the royal houses of England and Austria. He was interested in science and kept himself informed of the most recent advances in science, but did not have the time or equipment to do experimental work himself.

Jan Ingen-Housz
(Public Domain)

Through his reading, Ingen-Housz came to know about the work of Joseph Priestley on different kinds of gases (yes, Priestley again!). One experiment of Priestley’s particularly caught his imagination.

Priestley stumbles upon the action of plants on air

It was well known at the time that a candle covered by a glass jar got extinguished in a few seconds. Remember, this was before the modern understanding of oxygen and combustion, so Priestley and his contemporaries thought of it as burning “reducing the quality of air”. They knew that air in which a candle had burned out could not support life either.

This made Priestley wonder why it was that the air in nature did not permanently “go bad”. So many animals and human beings breathed in it and numerous forest fires burned year after year. What was nature’s secret way of purifying the air and making it breathable again?

In August 1771, Priestley carried out several experiments in his attempt to answer this riddle, some of which might seem laughable to us today. In one such experiment, Priestley kept a mint plant in a jar in which a candle had burned out. After 10 days, he took the mint plant out, taking care to ensure that the air in the jar did not mix with the air outside. When he introduced a lighted candle into this jar, it continued to burn just as if the air in the jar had been fresh air from outside.

Priestley’s confusion and Ingen-Housz’s clarity

Priestley should have discovered photosynthesis at this stage, but he didn’t. He did write a report on his experiment, but when other scientists tried to replicate his experiment, they failed to get the same result. They wrote back to him saying they weren’t convinced, and when Priestley tried repeating his own experiment, his own results this time were mixed. His confidence was shaken, though he continued to believe that plants had the power to purify air.

(Any guesses what Priestley was missing?!)

Ingen-Housz had come to know of Priestley’s experiment in 1773, but it was only in 1779 that Ingen-Housz finally managed to take the vacation he had been longing for. For six long years he had turned around in his mind the question of plants’ action on air. And that had prepared him to grab the opportunity to do his own experiments in spectacular fashion.

In the summer of 1779, Ingen-Housz went to stay in the English countryside and in a short three-month period, completed over 500 experiments that would form the body of his book, Experiments Upon Vegetables.

Ingen-Housz made several key discoveries that collectively form the bulk of our modern understanding of photosynthesis. However, two specific insights stand out, since they dispelled the mists of confusion that clouded Priestley’s ambiguous experiments.

Ingen-Housz realised that plants ‘improve the quality of air’ only in the presence of sunlight. In the dark, they reduce the quality of air, just like animals do. Furthermore, he recognised that only the leaves of plants had the ability to improve the air, while other parts like roots, flowers and fruits breathed like animals did.

He also showed that most of the dry weight of the plants came from the components of air that were ‘fixed’ during this process. In other words, plants were mostly “solidified air”!

Fading away into oblivion

It’s interesting to wonder why we don’t remember Jan Ingen-Housz the way we do numerous other scientists who made momentous discoveries. That’s the subject of an entire paper that was presented at a conference of the European Philosophy of Science Association in 2007.

It seems that Ingen-Housz was a humble person, keen to avoid fame and preserve his anonymity. Also, though he formulated most of the concepts of what we understand as photosynthesis today, the term itself was coined much later, in 1893. Probably we don’t remember Ingen-Housz, because what he discovered did not have a name!

References

  1. Leonard K. Nash. Plants and the Atmosphere. Harvard Case Histories in Experimental Science.
  2. Geerdt Magiels. Dr. Jan Ingen-Housz, or why we don’t know who discovered photosynthesis. 1st Conference of the European Philosophy of Science Association.

Time for Science Education

In a previous post, I looked at resources from the mid-20th century, when history and philosophy of science had been at the centre of debates on science education. Later, probably as a consequence of the Space Race starting in the late 1950’s, a more technocratic view of science education took over and history of science was relegated to the status of an esoteric discipline.

In recent decades, Michael Matthews, professor at University of New South Wales, Sydney, has been at the forefront of reviving interest in the history and philosophy of science as an area of core relevance to science education. It is one of his books, Time for Science Education, that I wish to look at in this blog post.

If I ever get to meet Prof. Matthews, I would like to ask him if he intended a pun in the book title! But on the surface, the ‘time’ in the title refers to timekeeping and time measurement. The theme of the book is how the history of clocks and timekeeping can be used to teach science through a historical-investigative approach.

I realised for the first time on reading this book that the simple pendulum — ubiquitous and dealt with in an abstract way in the school curriculum — had a rich and complex history that was closely tied to the development of clocks. Beginning with Galileo’s simple ‘pulsilogium’ (a weight suspended by a thread of adjustable length) that he used as a medical student to count the pulse rate of patients, to the precision of John Harrison’s famed clocks that kept accurate time on rough seas, there is a lot to delve into about the deceptively simple pendulum than just the formula of its time period.

It was also a revelation for me that until around as late as the 15th century, there was no real unit of time. The period of daylight was often divided into 12 equal hours, which meant that a summer hour was longer than a winter hour. This was good enough for people to go about their daily lives effectively.

What changed the game was the beginning of the Age of Exploration, and the need to determine longitude accurately at sea. Latitude could be determined easily by noting the position of certain stars or the Sun, but longitude was a very tricky affair and often the difference between life and death for mariners. It was this new need that drove an intense and competitive search for an accurate timekeeping mechanism. The mechanical clocks that were invented as a result, are some of the most fascinating devices ever made by humans.

One of the questions that the book opened up for me in science teaching was about the value of bringing in historical-social-cultural connections to the topics that are taught. Apart from making the topic appealing to students having a wider range of personalities and interests, situating the scientific idea in its broader context seemed to me to serve an important purpose of broadening the students’ worlds and imagination. And that might be more important than mastering certain scientific concepts, especially for the vast majority who never learn science after school.

Time for Science Education is a fairly expensive academic publication, but a limited preview is available on Google Books, to take a peek at some of the chapters: https://www.google.co.in/books/edition/Time_for_Science_Education/JrcqBgAAQBAJ?hl=en&gbpv=1

Joseph Priestley — the Science Historian

Joseph Priestley is pretty well known as the discoverer of the gas we now call oxygen. He was a brilliant scientist and had a very methodical mind. His fame rests primarily on the series of researches into the chemical properties of different gases, collected together under three volumes called Experiments and Observations on Different Kinds of Air.

There is, however, a less widely known aspect of Priestley’s scholarship that is no less brilliant. He was one of the first persons to write complete histories of scientific disciplines.

In 1767, Priestley’s book The History and Present State of Electricity was published. It was a massive 500-page book that started with the ancient Greek knowledge of the attractive powers of amber. It made its way, through all the major milestones in the development of electrostatics, to the then recent experiments of his contemporaries and friends like Benjamin Franklin. The book contains numerous obscure and forgotten experiments that are just as intriguing as the more famous ones. Priestley also included some of his own experiments, as the subtitle suggests.

The cover page of Priestley’s book on electricity

The book was presumably well received, for Priestley soon followed it up with another book on history of science, this time on light. The History and Present State of Discoveries relating to Vision, Colour, and Light came out in 1772.

The book on light

The preface to the second book on light reveals Priestley’s thinking behind these massive projects.

In order to facilitate the advancement of all the branches of useful science, two things seem to be principally requisite. The first is, an historical account of their rise, progress, and present state; and the second, an easy channel of communication for all new discoveries. Without the former of these helps, a person… labours under great disadvantages… finding himself anticipated in the discoveries he makes.

p.i, Preface, Light

In the preface, Priestley goes on to say how the knowledge in each branch of science was so vast and scattered in numerous books and languages, that there was a pressing need for someone to put it all together. Priestley acknowledges that the success of the book on electricity motivated him, and now he intended to embark on a very ambitious project to write similar books in all major branches of science.

It will be seen, in the preface to the first edition of the history of electricity, that I then considered the history of all the branches of experimental philosophy as too great an undertaking for any one person; but, like the fox with respect to the lion, a nearer view has familiarised it to me, and I now look upon it not only without dread, but with a great deal of pleasure;…(and) as a very practicable business.

p.iii, Preface, Light

However, in spite of his enthusiasm and confidence, Priestley never wrote any more histories of science. Perhaps it was the research on gases that occupied his time and mind completely. Nevertheless, the two histories that he did write are both absolute gems and a valuable source of knowledge for students of science and science history even today.

Harvard Case Histories in Experimental Science

James Bryant Conant (1893-1978) was a chemist, educationist and diplomat who served as a president of Harvard University. Among various educational reforms he pushed for in his influential position, was a greater role for the history and philosophy of science in science education.

In 1948, Harvard University Press published two volumes consisting of eight case studies in the history of science, edited by Conant and others. In the introduction, Conant writes that they were “designed primarily for students majoring in the humanities or the social sciences.”

The thinking was that people from a variety of professions — such as policy makers, lawyers, businessmen, teachers, writers, etc. — could be called upon to evaluate the work of scientists. To be able to do this, they needed to have an understanding of how science worked.

But how do you understand how science works, without having mastered the latest scientific knowledge?

Conant and his co-editors chose stories of discovery from 18th and 19th century science for their case histories. These were narratives that anyone who had had a basic secondary school education in science could follow. And as Conant argues in the introduction, the underlying process of scientific inquiry had not changed much since the 18th century, although research institutions and scientific communication had become far more sophisticated.

I learnt about the Harvard Case Histories in my first year of teaching. I was excited to find used copies available on Amazon’s US website. They were old copies discarded by some university library and I paid $1 for the books and $25 for the shipping! I devoured the case histories and found fascinating ways to use the material to actually teach science in school. I’ll write more about those explorations later, but this post is about the books themselves.

Volume 1 has four case studies in the physical sciences:

  1. Robert Boyle’s experiments with vacuum and air pressure
  2. Phlogiston theory and the chemical revolution
  3. Development of heat and temperature as distinct concepts
  4. The development of the atomic-molecular theory including the question of atomic mass

Volume 2 has three case studies in the life sciences and one in the physical sciences:

  1. The discovery of photosynthesis
  2. Pasteur’s study of fermentation
  3. Pasteur’s and Tyndall’s study of spontaneous generation
  4. The development of the concept of electric charge – early experiments up to Coulomb

The digital copies are freely accessible on Internet Archive. The books must still be in copyright, but I suppose they have been made available with permission from the publishers, being out of print since 1957. Internet Archive must surely have done their homework before making it available.

Volume 1: https://archive.org/details/harvardcasehisto010924mbp
Volume 2: https://archive.org/details/in.ernet.dli.2015.60093

Tribute to Hans Christian Oersted, 200 Years after His Experiment – Part II

In Part I of this tribute, we looked at some of the background of Oersted’s famous experiment. We saw that Oersted was philosophically inclined to believe in the existence of a link between electricity and magnetism, but had not actually formulated any hypothesis or experiment to specifically investigate it. We touched upon the fact that Oersted observed a slight deflection of the magnetic needle in the lecture experiment, but he kept it aside and did not immediately communicate it to anyone.

Oersted wanted to be sure that the movement of the magnetic needle was not due to any other causes – for example, a stray electrostatic charge that could have caused any needle, even non-magnetic, to deflect. He had been using a battery that was only moderately strong, so he set about building a much larger and more powerful battery. This took several weeks, and required the help of craftsmen who had the relevant skills.

Remember that Oersted believed in the unity of all the forces of nature, not just electricity and magnetism. In his mind’s eye, it was only when a current made a wire red hot that it emitted a magnetic force along with the heat and light. So in his experiment he was using a very thin platinum wire with a high resistance to get a glow on passing a current.

Oersted imagined the magnetic effect of the current to be radiating outwards from the wire, just like heat and light. This had a profound influence on where Oersted would have kept the magnetic needle to check for deflections, as illustrated in the figure below.

If the magnetic field had radiated outwards from the wire as Oersted imagined it, he would have expected the needle to show the maximum deflection when the needle was kept beside the wire, forming a horizontal plane.

This was an accidental factor that greatly diminished his chances of seeing a proper deflection. As we know today, the magnetic field lines form a circular loop around the wire. A needle kept beside the wire would not have deflected much, since the magnetic field lines at that point would have been in a vertical plane, perpendicular to the needle’s plane of free rotation.

Oersted’s best chance of seeing a large deflection would have been to keep the needle right above the wire, but in his conception of a radially emitted magnetic force, that was the position in which the needle would deflect the least!

Even after he got his new powerful battery, we see that Oersted was labouring under two hypotheses that stacked the odds against him:

  1. The magnetic effect was produced only when the wire emitted heat and light as well.
  2. The magnetic effect was emitted by the wire radially outward.

The first hypothesis made Oersted use extremely thin wires in his circuit to get the wire glowing. This meant that the current he got from the battery was far weaker than it could have been, if he hadn’t been thrown off track by his need to make the wire red hot.

Oersted did not record when and how exactly he realised that the wire need not be red hot. We can only surmise that he most likely discovered it by accident. He must have moved the compass around and must have seen the needle remain deflected by the same angle even near one of the connecting leads far away from the red hot wire.

Once he realised that he did not need a red hot wire, Oersted started using a thicker wire that could carry a stronger current. This led him to soon recognise that the direction of the magnetic force was not as he had imagined it to be, but actually formed a circular loop around the current-carrying wire.

By this point, Oersted had understood the gravity of his discovery. He naturally didn’t want to be beaten to it by anyone else, so he rushed to write a report of his experiments and sent it to several scientists across Europe on 21 July 1820.

What happened afterwards is much better known – the invention of the electromagnetic motor and generator, electromagnets and the telegraph – all of which can be traced back to this seemingly insignificant and academic experiment.

As we complete 200 years of this experiment, I feel that this is a rich story to delve into with students. Nahum Kipnis, an eminent science historian and educator, recommends getting students to actually repeat Oersted’s experiment as he did it, first with red hot wires and let them refute Oersted’s hypotheses and discover the circular magnetic field lines themselves. It would fit right into a historical-investigative approach to teaching electromagnetism.

Reference

  1. Nahum Kipnis. Chance in Science: The Discovery of Electromagnetism by H.C. Oersted. https://www.academia.edu/10253171/Chance_in_Science_The_Discovery_of_Electromagnetism_by_H_C_Oersted

Tribute to Hans Christian Oersted, 200 Years after His Experiment – Part I

Hans Christian Oersted

This year, a bicentennial passed by, probably without the celebration and commemoration it deserved. A search of ‘Oersted’s experiment 200th anniversary’ throws up barely half a dozen pages, most of them based in Oersted’s native Denmark. Almost all physics textbooks mention his experiment in the introduction to electromagnetism, but I wonder if in most people’s minds it is just that – simply a prelude to all the other great discoveries made by Michael Faraday and others.

In the prevailing confusion at the height of the lockdown, I myself missed the date – 21 April – when, during a lecture-demonstration, Oersted first noticed a magnetic needle move when a current was switched on.

As my little tribute to the monumental discovery, in this post I look more closely at the details of the story. Was it just an accidental discovery as most modern textbooks narrate it? Or was Oersted expecting to find a link between electricity and magnetism? I dive into an excellent article written by science historian and educator Nahum Kipnis to find out.

As early as 1812, Oersted had written about his belief in the unity of the forces of nature – heat, light, chemical affinity, electricity and magnetism. This was a purely metaphysical speculation arising from his worldview of nature as having order and symmetry. It did not make Oersted formulate any testable hypothesis or design any experiment for the next eight years.

His interest in this topic was revived by a course he had to teach at the University of Copenhagen in 1819-20. In April, he was scheduled to deliver a lecture on new discoveries in physics and chemistry to a group of advanced students. Oersted planned to discuss various connections between electricity, magnetism and galvanism (the group of phenomena related to the electrochemical battery discovered by Volta).

This was not an entirely new area of research, for attempts to find links between static electricity and magnetism, and between magnetism and chemistry, had been going on since the mid 1750s. Some scientists had succeeded in weakly magnetising a steel needle by passing a discharge from a Leyden jar (a primitive capacitor made from a glass jar) through the needle.

There is considerable debate among science historians about what actually happened in that legendary lecture. To make things murkier, the supposed eye-witness account of Christopher Hansteen, a student of Oersted’s, conflicts with Oersted’s own writings.

Without getting into the messy details, it seems apparent that Oersted speculated in front of his student audience that the current in the circuit might have an effect on a magnetic needle. There doesn’t seem to be any record of Oersted having tried out this experiment beforehand. But it begs the perplexing question of why an esteemed professor would risk his reputation by floating unverified ideas in a lecture to a group of advanced students. Maybe it was simply a maverick moment that teachers sometimes have when they share their excitement with students!

As everyone familiar with the experiment knows, Oersted noticed a slight deflection of the magnetic needle on closing the circuit. He was not particularly convinced by this observation, and did not consider it worthy of communicating to other scientists right away.

In fact, Oersted slept on this observation for almost three months. However, on 21 July, Oersted hastily dispatched printed copies of his report of the experiment to several scientists and institutions.

In the second part of this tribute, I will look at how Oersted made sense of his discovery and what was it that he did, leading up to his realisation that he had chanced upon a new scientific fact that was very significant.

Also read Part II.

Andre-Marie Ampere and the Current through a Battery

Ampere’s experiments on the attraction and repulsion of two current-carrying wires depending on the direction of the currents, are well known. I recently learned about another experiment of his – seemingly simple and perhaps trivial – but actually very significant. It was in the book ‘Ampere’s Electrodynamics’ by the brilliant Brazilian scholar A. K. T. Assis, that I read about this experiment.

It was September of 1820. A few months earlier, in April, Hans Christian Oersted had demonstrated the effect of an electric current in a wire on a magnetic compass kept near it. Ampere came to know of this experiment and repeated it.

Ampere’s unique addition to Oersted’s experiment was to check whether there was a similar effect on a compass needle kept near the battery. The battery widely used at the time was a trough battery – a large rectangular box having several compartments filled with acid in which pairs of metal plates were dipped.

Ampere’s experiment: A compass needle was deflected the same way when kept above the battery

The magnetic needle was deflected in the same way when kept above the battery, as it would have been if kept above the wire. Ampere showed that a current flowed through the battery. And that this current was in the same direction as the current in the wire, forming a closed loop.

That’s obvious to us today, but we must realise that this was less than three decades since Volta first invented the battery and how it worked was still a mystery to everyone. This was a time when the most familiar electrical phenomena were all electrostatic in nature. The only other source of electricity scientists knew about were a Leyden jar (a capacitor made from a glass jar) which gave brief bursts of current.

Against this backdrop, what Ampere discovered raises more questions than answers. If the current flowed in a closed loop in the circuit, that meant the current inside the battery flowed from the negative terminal to the positive terminal! This was the opposite of the direction you would expect the current to flow if it were driven by electrostatic forces.

So, Ampere indirectly proved that there were non-electrostatic forces in the battery that caused the current.

What caused a battery to produce a current had already become a raging debate at the time and wouldn’t be settled until over half a century later. That is a topic that deserves several posts, and I’ll return to later.