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Faraday Motor – 1821

Few inventions have shaped technology as much as the electric motor, but the very first version — the Faraday motor — didn't look anything like the modern motor.

Self-taught British scientist Michael Faraday (1791 – 1867) built the first primitive motor about 1821, shortly after the discovery that an electric current produces a magnetic field.

His motor featured a stiff wire in a container of mercury (a metal that is liquid at room temperature and an excellent conductor) and a permanent bar magnet in the center of the container. He sent electricity through the wire and created a magnetic field around it. This field interacted with the field around the magnet and caused the wire to rotate around the magnet.

Even though it had no practical application, Faraday's invention was the first step in the evolution of the electric motor.

Other scientists quickly made improvements on it. A few months later, British physicist William Sturgeon developed the first rotary electric motor, a forerunner of the present-day direct-current motor.

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Allison Marsh is a professor at the University of South Carolina and codirector of the university's Ann Johnson Institute for Science, Technology & Society.

Michael Faraday created this model of his electric motor in 1822, a year after his discovery.

In 1820, the Danish physicist Hans Christian Ørsted threw electromagnetic theory into a state of confusion. Natural philosophers of the day believed that electricity and magnetism were two distinct phenomena, but Ørsted suggested that the flow of electricity through a wire created a magnetic field around it. The French physicist André-Marie Ampère saw a demonstration of Ørsted's experiment in which an electric current deflected a magnetic needle, and he then developed a mathematical theory to explain the relationship.

English scientist Michael Faraday soon entered the fray, when Richard Phillips, editor of the Annals of Philosophy, asked him to write a historical account of electromagnetism, a field that was only about two years old and clearly in a state of flux.

Faraday was an interesting choice for this task, as Nancy Forbes and Basil Mahon recount in their 2014 book Faraday, Maxwell, and the Electromagnetic Field . Born in 1791, he received only a barebones education at church school in his village of Newington, Surrey (now part of South London). At the age of 14 he was apprenticed to a bookbinder. He read many of the books he bound and continued to look for opportunities to learn more. In a fateful turn of events, just as Faraday's apprenticeship was coming to an end in 1812, one of the bookbinder's clients offered Faraday a ticket to Humphry Davy's farewell lecture series at the Royal Institution of Great Britain.

Davy, just 13 years older than Faraday, had already made a name for himself as a chemist. He had discovered sodium, potassium, and several compounds and invented the miner's safety lamp . Plus he was a charismatic speaker. Faraday took detailed notes of the lectures and sent a copy to Davy with a request for employment. When a position opened as a chemistry assistant at the Royal Institution, Davy hired Faraday.

Davy mentored Faraday and taught him the principles of chemistry. Faraday had an insatiable curiosity, and his reputation at the Royal Institution grew. But when Phillips asked Faraday to write the review article for the Annals , he had only dabbled in electromagnetism and was a bit daunted by Ampère's mathematics.

At heart, Faraday was an experimentalist, so in order to write a thorough account, he re-created Ørsted's experiments and tried to follow Ampère's reasoning. His "Historical Sketch of Electro-Magnetism," published anonymously in the Annals , described the state of the field, the current research questions and experimental apparatus, the theoretical developments, and the major players. (For a good summary of Faraday's article, see Aaron D. Cobb's "Michael Faraday's 'Historical Sketch of Electro-Magnetism' and the Theory-Dependence of Experimentation," in the December 2009 issue of Philosophy of Science .)

While reconstructing Ørsted's experiments, Faraday was not entirely convinced that electricity acted like a fluid, running through wires just as water runs through pipes. Instead, he thought of electricity as vibrations resulting from tension between conducting materials. These thoughts kept him experimenting.

Faraday observed the circular rotation of a wire as it was attracted and repelled by magnetic poles. "Very satisfactory," he wrote in his notebook.

On 3 September 1821, Faraday observed the circular rotation of a wire as it was attracted and repelled by magnetic poles. He sketched in his notebook a clockwise rotation around the south pole of the magnet, and the reverse around the north pole. "Very satisfactory," he wrote in his entry on the day's experiment, "but make more sensible apparatus."

The next day, he got it right. He took a deep glass vessel, secured a magnet upright in it with some wax, and then filled the vessel with mercury until the magnetic pole was just above the surface. He floated a stiff wire in the mercury and connected the apparatus to a battery. When a current ran through the circuit, it generated a circular magnetic field around the wire. As the current in the wire interacted with the permanent magnet fixed to the bottom of the dish, the wire rotated clockwise. On the other side of the apparatus, the wire was fixed and the magnet was allowed to move freely, which it did in a circle around the wire.

For a helpful animation of Faraday's apparatus, see this tutorial created by the National High Magnetic Field Laboratory. And if you'd like to build your own Faraday motor, this video will walk you through it:

Although a great proof of concept, Faraday's device was not exactly useful, except as a parlor trick. Soon, people were snatching up pocket-size motors as novelty gifts. Although Faraday's original motor no longer exists, one that he built the following year does; it's in the collections of the Royal Institution and pictured at top. This simple-looking contraption is the earliest example of an electric motor, the first device to turn electrical energy into mechanical motion.

The fallout from Faraday's invention

Faraday knew the power of quick publication, and in less than a month he wrote an article, "On Some New Electromagnetic Motions and the Theory of Electromagnetism," which was published in the next issue of the Quarterly Journal of Science, Literature, and the Arts. Unfortunately, Faraday did not appreciate the necessity of fully acknowledging others' contributions to the discovery.

Within a week of publication, Humphry Davy dealt his mentee a devastating blow by accusing Faraday of plagiarism.

Davy had a notoriously sensitive ego. He was also upset that Faraday failed to adequately credit his friend William Hyde Wollaston , who had been studying the problem of rotary motion with currents and magnets for more than a year. Faraday mentions both men in his article, as well as Ampère, Ørsted, and some others. But he doesn't credit anyone as a collaborator, influencer, or codiscoverer. Faraday didn't work directly with Davy and Wollaston on their experiments, but he did overhear a conversation between them and understood the direction of their work. Plus it was (and still is) a common practice to credit your adviser in early publications.

When Faraday's reputation began to eclipse that of his mentor's, Faraday made several missteps while navigating the cutthroat, time-sensitive world of academic publishing.

Faraday fought to clear his name against the charge of plagiarism and mostly succeeded, although his relationship with Davy remained strained. When Faraday was elected a fellow of the Royal Society in 1824, the sole dissenting vote was cast by the society's president, Humphry Davy.

Faraday avoided working in the field of electromagnetism for the next few years. Whether that was his own choice or a choice thrust upon him by Davy's assigning him time-consuming duties within the Royal Institution is an open question.

One of Faraday's assignments was to salvage the finances of the Royal Institution, which he did by reinvigorating the lecture series and introducing a popular Christmas lecture. Then in 1825 the Royal Society asked him to lead the Committee for the Improvement of Glass for Optical Purposes, an attempt to revive the British glass industry, which had lost ground to French and German lens makers. This was tedious, bureaucratic work that Faraday undertook as a patriotic duty, but the drudgery and relentless failures took a mental toll.

Faraday's experiments of 1831 yield the transformer and the dynamo

In 1831, two years after Davy's death and after the completion of Faraday's work on the glass committee, he returned to experimenting with electricity, by way of acoustics. He teamed up with Charles Wheatstone to study sound vibrations. Faraday was particularly interested in how sound vibrations could be seen when a violin bow is pulled across a metal plate lightly covered with sand, creating distinct patterns known as Chladni figures. This video shows the phenomenon in action:

Faraday looked at nonlinear standing waves that form on liquid surfaces, which are now known as Faraday waves or Faraday ripples. He published his research, "On a peculiar class of acoustical figures; and on certain forms assumed by groups of particles upon vibrating elastic surfaces," in the Royal Society's Philosophical Transactions .

Still convinced that electricity was somehow vibratory, Faraday wondered if electric current passing through a conductor could induce a current in an adjacent conductor. This led him to one of his most famous inventions and experiments: the induction ring . On 29 August 1831, Faraday detailed in his notebook his experiment with a specially prepared iron ring. He wrapped one side of the ring with three lengths of insulated copper wire, each about 24 feet (7 meters) long. The other side, he wrapped with about 60 feet (18 meters) of insulated copper wire. (Although he only describes the assembled ring, it likely took him many days to wrap the wire. Modern experimenters who built a replica spent 10 days on it.) He then began charging one side of the ring and looking at the effects on a magnetic needle a short distance away. To his delight, he was able to induce an electric current from one set of wires to the other, thus creating the first electric transformer.

Faraday continued experimenting into the fall of 1831, this time with a permanent magnet. He discovered that he could produce a constant current by rotating a copper disk between the two poles of a permanent magnet. This was the first dynamo, and the direct ancestor of truly useful electric motors.

Two hundred years after the discovery of the electric motor, Michael Faraday is rightfully remembered for all of his work in electromagnetism, as well as his skills as a chemist, lecturer, and experimentalist. But Faraday's complex relationship with Davy also speaks to the challenges of mentoring (and being mentored), publishing, and holding (or not) personal grudges. It is sometimes said that Faraday was Davy's greatest discovery, which is a little unfair to Davy, a worthy scientist in his own right. When Faraday's reputation began to eclipse that of his mentor's, Faraday made several missteps while navigating the cutthroat, time-sensitive world of academic publishing. But he continued to do his job—and do it well—creating lasting contributions to the Royal Institution. A decade after his first breakthrough in electromagnetism, he surpassed himself with another. Not bad for a self-taught man with a shaky grasp of mathematics.

Part of a continuing series looking at photographs of historical artifacts that embrace the boundless potential of technology.

An abridged version of this article appears in the September 2021 print issue as "The Electric Motor at 200."

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Allison Marsh is a professor at the University of South Carolina and codirector of the university's Ann Johnson Institute for Science, Technology & Society. She combines her interests in engineering, history, and museum objects to write the Past Forward column, which tells the story of technology through historical artifacts.

If you ever get to London, England, check out Faraday's lab on display at the the Royal Institute in Mayfair. Or check it out online,... https://www.rigb.org/our-history/michael-faraday/magnetic-laboratory

What a piece of history.

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In the SPARK Museum, a trove of early electric motors

On display at The SPARK Museum of Electrical Invention are myriad devices that tell the exciting story of electrical history, including a string of devices that walk visitors from the early thought experiments of Michael Faraday to the electric induction motors of Nikola Tesla:

Henry Reciprocating Motor: Along with Michael Faraday, Joseph Henry is often referred to as a founding father of the electrical industry. In 1831, Henry created one of the earliest machines to produce motion from electromagnetism. Also one of the earliest electric motors, Henry’s device consisted of a long electromagnet perched on a pole, rocking back and forth from polarity changes caused by the magnet connecting with battery leads on each side. Henry’s work was the foundation for Thomas Davenport’s 1834 electric motor, which was used to operate model cars and trains. One of the two electromagnets from Henry’s original machine is on display at The SPARK Museum.

Pixii Dynamo: In 1832, Frenchman Hippolyte Pixii used Faraday’s principles to build the first direct current dynamo, or electrical generator. The device consists of a permanent magnet spun around by use of a hand-operated crank. As the magnet rotates, its poles swing by a piece of iron wrapped in wire, producing small pulses of alternating current with each passing. To convert the pulses into direct current, Pixii developed what’s known as a commutator. The Pixii Dynamo, the first device to generate both AC and DC, is the actual patent model submitted by Pixii. It’s truly a one-of-a-kind item.

Gramme Dynamo: In 1871, Zenobe Theophile Gramme invented his industrial-strength dynamo, taking the devices from the level of electronic experimentation in Pixii’s day to the level of productive machinery. Gramme’s invention was the first to be used for manufacturing and farming, and together with French engineer Hippolyte Fontaine, Gramme founded a factory to produce the machine and several other devices. Even today, the Gramme dynamo serves as the basis for the design of many direct-current electric motors.

Yes, all of these amazing devices are part of the massive display at our science and history museum in Bellingham, WA. Where else, outside of the Smithsonian in the other Washington, can you see such an extensive collection of electrical history?

What are you waiting for? Come check out The SPARK Museum of Electrical Invention this weekend.

How Faraday Invented The Motor And Annoyed His Mentor

Why would inventing a motor irritate anyone?  And how did Faraday invent the motor in the first place?  Well, I’ll tell you and along the way I will talk about a strange theory of spiraling currents, a misunderstanding of electromagnetic forces, and a useless motor. 

Table of Contents

Oersted’s discovery, humphry davy and faraday, faraday’s 1821 experiment, why faraday’s motor was controversial, video script download.

In 1820, a Danish man named Oersted made a remarkable discovery.  When current runs through a wire it can make compass point in a circle around the wire!  Now a compass is just a thin magnet on a pivot, so Oersted had proved that electricity and magnetism are linked.

What was incredibly confusing to people was that the current went a straight line and the magnets made circles around the wire.  Oersted’s solution was that maybe the current was really spiraling down the wire. 

He even made it more complex then that, where a positive current spiraled one way and moves the north end of the compass and a negative current spiraled the other way and moves the south end of the compass!  Whew.

Humphry Davy and Farada y

This brings us to England and men named Michael Faraday and his mentor Humphry Davy . 

Humphry Davy was a famous Chemist and laughing gas aficionado who was arguably the most famous scientist in all of Europe at the time.  Eight years previously, Davy had injured his eye and hired Michael Faraday, a young, uneducated and poor bookbinder’s apprentice as his assistant. 

By 1820, Davy was promoted to president of the Royal Institution of London and Faraday had been promoted to the position of “Chemical Assistant” and was conducting some of his research independently of Davy.  

Both Davy and Faraday (and frankly, every other scientist in Europe) heard about Oersted’s experiment and tried to figure out what it meant.  Davy wrote his brother that, “I have ascertained (repeating some vague experiments of Orsted’s) that the battery is a powerful magnet…I am deeply occupied in this.” 

Notice that Davy got an important fact wrong about Orsted’s experiment.  The battery is not a magnet!  It is tempting to think it must be as it often is in a similar shape to a bar magnet and the + and – signs seem so similar to the N and S of a magnet.

In fact, the battery isn’t magnetic, but the current in the wire is.  In April, Davy collaborated with his friend William Wollaston in this problem. 

Wollaston had agreed with Oersted that the current must spiral down the wire.  They spent many hours trying to come up with an experiment to demonstrate this spiraling motion, but to no avail. 

Supposedly, Faraday heard some of their discussions but never found them interesting enough to put in his notebook.  

In the summer of 1821, Faraday was asked to write a review of the latest developments in electricity for a journal. 

Through painstaking experiments Faraday determined that the wire wasn’t attracting either end of the magnet but instead orienting the entire magnet.  He also determined that the force was purely circular around the wire not spiraling as Oersted thought. 

He decided that, strange as it may seem, the current seemed to travel straight down the wire and somehow it made a circular force on a magnet around the wire. 

In return, Faraday also postulated that a magnet also made a circular force on a wire around it.  In other words,  “a wire ought to revolve round a magnetic pole and a magnetic pole round the wire”.  

Faraday began looking for a way to demonstrate that a current carrying wire will feel a force in a circle around a magnet. 

On September 3rd, 1821 he created a simple experiment in his laboratory to demonstrate this force.  He had a wire drop down on a cup full of mercury (mercury is a conducting fluid) with a permanent bar magnet in the center. 

When he closed the switch the wire spun continuously.  Supposedly, Faraday shouted, “There they go! There they go! We have succeeded at last!” 

Technically, Faraday had just invented the electric motor as an electric motor is a device that changes electrical energy into motion.  Of course, it wasn’t a particularly practical motor as it didn’t do any useful work (unless you want to electrically stir mercury). 

Luckily, Faraday didn’t invent the motor to do any work.  He invented it to demonstrate that the current moves straight down the wire and the magnetic force is circular around the wire. 

As a motor, it was useless, as a demonstration of the nature of magnetic fields it was quite efficient.    

Faraday published his work on October 1 st , 1821 to great acclaim.  But within a week, he heard rumors that people were saying he plagiarized his material.  The person shouting the loudest was his former boss and mentor, Humphrey Davy!  

Faraday wrote to Wollaston, “I am anxious to escape from unfounded impressions against me and if I have done any wrong that I may apologize for it.”  Wollaston wrote back and claimed to be unoffended; “you have no occasion to concern yourself much about the matter.”  However, Wollaston didn’t publically defend Faraday and Davy publically attacked him.  

It is hard to know, almost 200 years after the fact, why people did what they did and how they felt about it. 

Most modern researchers feel that Davy was jealous of his protégée’s success and felt that Faraday was too low class and uneducated to be an independent researcher. 

Davy was from a middle class background but had been knighted as a baron in recognition of his scientific work.  Therefore Davy might have been class conscious in a way that a person who has risen far from middle class beginnings could be. 

However, it is also possible that Davy felt justified in his anger.  Faraday was a person that Davy had plucked from obscurity and he did not give credit to his benefactor. 

And it is true that Davy and Wollaston had been trying to make a spinning device before Faraday did (although with a different motivation).  Finally, it isn’t clear that Davy really understood what Faraday was proving with his experiments. 

Davy’s brother stated that his objections to Faraday were “an act of justice to Dr. Wollaston”, and it is quite possible that Davy felt that way for the rest of his life.

In May of 1823, Faraday was nominated to be a fellow of the Royal Institute to the strong objection of Davy (the secret vote was nearly unanimous with only one dissenter, probably Davy). 

In 1826, Davy fell very ill from using too much laughing gas or from inhaling dangerous chemicals in the laboratory and resigned from his job as a Chemist.  Davy passed away three years later.  

Meanwhile, Faraday was eager to continue his studies of electricity but instead he was basically forced by the government to study how to make better optical glasses (a study that he found particularly fruitless, stating that the only results were his own “nervous headaches”).  Therefore, Faraday was unable to return to electricity until 1831.

The first person to really take Faraday’s idea to the next level was a newly retired soldier and boot maker named William Sturgeon.  Sturgeon actually invented one of the first practical motors in 1834. 

First, however, he focused on another thing Faraday mentioned in his paper, that a helix of wire acts like a bar magnet.

Video Script

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Michael Faraday

By Sujay Kalathoor Q02

Michael Faraday was an English scientist who's discovery's greatly influenced the fields of electromagnetism and electrochemitry.

• 1 Biography
• 2 Discoveries
• 3.1 Faraday's Law of Magnetic Inductance
• 3.2 Electric Motors
• 3.3 Diamagnetism
• 4 Applications and Connectedness
• 5.1 External links
• 6 References

Faraday was born in London in 1791 to a poor family, meaning he only received a basic education. He got a job as a bookbinder's apprentice at age 14, where he would read books on scientific subjects to teach himself a wide array of topics. Faraday furthered his career by contacting the chemist Humphry Davy to become his chemical assistant in 1813. With Davy, Faraday traveled around Europe meeting other famous scientists and fine-tuning his own ideas for research. When Faraday and Davy returned in 1815, Faraday continued performing experiments and conducting research, making many crucial discoveries and starting programs such as the Royal Institution's Friday Evening Discourses and Christmas Lectures, which still continue to this day. Faraday's health started to deteriorate in the 1840's, which lessened his ability to do further research. He died in 1867. The farad, a unit for capacitance, is named in his honor.

Discoveries

Faraday's contributions to modern science lie mainly in the field of electromagnetism and electrochemistry. He discovered the relationship between electricity and magnetism, called electric inductance, which can be defined by an equation known as Faraday's Law. He also discovered diamagnetism, where materials oppose applied magnetic fields with their own fields, invented the first electrical motor, and first observed electrolysis, where electricity drives chemical reactions. Among other things, Faraday also discovered the molecule benzene and popularized terms like cathode, anode, and ion, which are used in everyday chemistry today.

Major Contributions to Physics

Faraday's law of magnetic inductance.

One of Michael Faraday's greatest discovery's is magnetic inductance, or the relationship between a changing magnetic field and a voltage. Basically, any change in a magnetic field near a coil in a wire will cause a voltage to run in that coil. That change in magnetic field could be a change in field strength or simply a change in position of the field relative to the coil. The formula is [math]\displaystyle{ emf = -N{\frac{d{Φ}}{dt}} }[/math] , where emf is the induced voltage, N is the number of loops in the coil, and Φ is the magnetic flux. Magnetic flux is defined as [math]\displaystyle{ Φ = BA }[/math] , where B is the magnitude of the magnetic field, and A is the area of the loop. Flux is any measurable field through a surface. Any time there is a change in magnetic flux with respect to time across the coil, a voltage is induced in that coil, causing current to flow.

Electric Motors

In 1822, Faraday invented the first electric motor. An electric motor derives its mechanical work from electricity, and Faraday used the discovery of magnetic inductance to create forces that moved a wire. Basically, Faraday hung a wire into a glass bowl filled with mercury and a magnet. Mercury is a great conductor of electricity, so he connected a battery to the apparatus which sent current flowing through the wire. Using the principles of inductance, Faraday predicted that the wire would then induce a magnetic field in a circular loop around itself. This magnetic field would interact with the magnetic field caused by the magnet at the bottom of the bowl, creating forces that would cause the wire to spin. This was a rudimentary motor, but since that time companies and engineers have perfected Faraday's model. Electric motor's are used in everyday items such as cars, hair dryers, lawn mowers, washing machines, vacuum cleaners, and more.

Diamagnetism

Another of Faraday's important discoveries is diamagnetism. Diamagnetic materials oppose an applied magnetic field with a weak, induced magnetic field of its own. The material does this by alligning its electron clouds in such a way that the current of those electrons creates a magnetic field in the opposite direction of the applied field. All materials have diamagnetic properties. Conductors are actually strong diamagnets, as they induce strong opposing magnetic fields.

Applications and Connectedness

• The most obvious connection Michael Faraday has to Physics II is the applications of Faraday's Law to Inductance .
• Faraday's Law can be used to determine both the magnitude and direction of the Curly Electric Fields resulting from the changing magnetic field and current in a loop.
• Faraday's Law is used to power electrical motors
• Motional Emf using Faraday's Law is where a voltage is induced in a rod by moving that rod on a metal track through a constant magnetic field
• Transformers (Physics) also apply Faraday's Law
• Lenz's Law was discovered as a result of Faraday's work
• Curly Electric Fields
• Motional Emf using Faraday's Law
• Transformers (Physics)

External links

http://www.britannica.com/biography/Michael-Faraday

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magpr.html#c2

http://www.rigb.org/our-history/iconic-objects/iconic-objects-list/faradays-motor

http://www.imsc.res.in/~indu/JM/2010/nov.html

http://physics.stackexchange.com/questions/88841/deriving-expression-for-motional-emf

https://nationalmaglab.org/education/magnet-academy/history-of-electricity-magnetism/museum/faraday-motor-1821

• Notable Scientists

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Faraday Motor

posted on 30 Jan 2013 by guy last changed 23 Apr 2014

In 1821, the English scientist Michael Faraday designed and built the first electric motor. His design is one in the class of homopolar motors (see the lesson on Minimalist Motors for more discussion) and is one of the simplest motor designs to date. His original version used a copper rod that rotated in a pool of mercury around a central magnet. Although it's easy enough to build Faraday's original design, mercury is a toxic substance that we prefer to keep out of the classroom. In this lesson, we construct a less toxic modern version of Faraday's motor out of everyday materials. For basic principles of operation describing how this and other motors work, please see our lesson on A Survey of Simple Electric Motors .

construction

There are many implementations of Faraday's motor available; one of the best setups I've seen is by Arbor Scientific , shown in the video above. The materials you will need are:

• two plastic 2-liter soda bottles (or one soda bottle and one clear glass)
• connecting wires (alligator clip leads preferred)
• one or two 9V batteries
• strong disk magnets (preferably Neodymium magnets)
• modeling clay (optional)
• stiff, solid core wire (14 to 10 gauge — 1.5 to 2.5 mm diameter) or coat hanger for the wire in the straw
• stiff, solid core copper or aluminum wire (18 to 15 gauge) for the hanging rod
• aluminum foil
• two small paper clips
• a plastic soda straw
• optional switch
• optional battery caps (see Figures 2 and 3)

The basic construction steps are outlined in the video. I add only a few comments here.

The solid copper or aluminum wire is sometimes a little difficult to come by in the thicker gauges required for the wire inside the plastic straw, and can't always be found in the local hardware store. Look for solid core grounding wire, or galvanized utility wire. Another option is copper or aluminum Bonsai tree training wire. Still another option is a piece of steel wire from a coathanger. Use a coathanger with a cardboard tube across the bottom since the end of that wire already has a nice hook in it, and the cardboard tube can replace the plastic straw.

The hanging copper rod must be non-magnetic (copper or aluminum) and should be cut to hang just above the bottom of the container. It should reach down past the sides of the magnet stack. This wire can be thinner. Anything from 18 to 15 gauge (1 to 1.5 mm diameter) should work.

The video suggests cutting the bottom off of a 2-liter soda bottle to act as the container for the pool of saltwater. You may wish to use a taller container in order to explore what happens as more salt water is added (see the discussion in "questions to ponder" below). In that case, cut just the top off the bottle and use a tall container; it can always be cut down later. The 2-liter bottle that serves as the stand should be mostly filled with water to weigh it down.

When preparing the saltwater, keep in mind that more salt generally supports more current, up to a point. At room temperature, roughly 20% salt by weight makes a saturated solution. You may wish to start with less salt, or no salt, to see what happens as additional salt is added to the solution (see the discussion in "questions to ponder" below). Fill the container to about the level of the top of the magnets or a little higher for best results.

The thickness of the disk magnets does not matter significantly; there should be enough of them to form a stack 2 cm or more in height. The magnet diameter needs to be small enough so that the copper rod revolves around it without touching. A diameter between 3 and 5 mm (1/8 to 1/4 inch) works well.

The modeling clay is only used to support the stack of magnets on the uneven bottom of the soda bottle. You can do without the clay if you stick one of the magnets underneath the soda bottle to hold the other magnets in place. If you are using a clear flat-bottom glass instead, you may not need even that. Alternatively, chewing gum may work, which has the advantage of engaging an entire class in the preparation of the gum. And NO, they cannot have the gum back after it has been used in the experiment.

Alligator leads are very convenient for quick connections, and are available from many sources, but tape and flexible insulated wire works just as well.

You may wish to use a switch in the circuit, like the single-pole, single throw knife switch shown in the video. It is not necessary however; to turn off the motor you can always disconnect a wire.

Connect the circuit and watch it go.

If you have connected the circuit as shown in the video, electrons will flow from the negative terminal of the battery, through through the paper clips and the copper rod. That electric current will be transferred through the saltwater, to the aluminum foil (though not as free electrons — see the relevant discussion in "questions to ponder" below), and back to the positive terminal of the battery. As the electrons flow down the copper rod, they feel a force from the magnetic field generated by the stack of magnets.

This force derives from the notion that an electric current in a wire produces a magnetic field (a fact discovered by Hans Christien Ørsted and André-Marie Ampère in 1820, and described by Ampère's Law as the principle behind the electromagnet). A current-carrying wire therefore feels a force from any nearby magnet in the same way that two magnets feel forces from each other. The force felt by a current in a magnetic field is called the Lorentz force (see the lessons on Classroom Rail Gun and  A Survey of Simple Electric Motors for more on the Lorentz force), and was derived by the Dutch scientist Hendrik Lorentz in 1892.  In our Faraday motor, the electrons moving down the copper rod feel a Lorentz force from the magnets, which pushes them in a clockwise or counter-clockwise direction around the stack, depending on whether the magnets are arranged with north poles up or down.

For the geek who wants to precisely calculate the direction of the Lorentz force, the Java demo created by the clever folks at the National High Magnetic Field Lab shows the setup of the Faraday motor with the magnetic field lines drawn in. Knowing the magnetic field, the current direction, and the right hand rule (a useful mnemonic for determining the direction of a Lorentz force), one can determine exactly what direction the force is pointing.

Students should be encouraged to modify the parameters of the motor to see how various changes affect the operation of the motor. Some suggestions are:

• add more salt to the solution
• use fewer or more magnets
• reverse the leads on the battery
• turn the magnets upside down
• use a 1.5 volt D cell battery instead of a 9 volt battery
• use two 9 volt batteries connected in series (see Figure 2)
• use two 9 volt batteries connected in parallel (see Figure 3)
• add more saltwater to the container

questions to ponder

• What happens if we turn the magnets over or reverse the leads on the battery?

Naturally, if we turn the magnets over, we reverse the direction of the magnetic field lines. If we reverse the leads on the battery, we reverse the direction of current flow. In either case, we reverse the direction of all the forces. The motor will run backwards.

• What happens if we use more batteries?

Keep in mind that the force on the movable rod depends on the strength of the magnet stack and the electric current flowing through the rod. More current leads to more force, and a faster motor. If we connect two batteries in series, we produce twice the voltage and push more current through the circuit. The motor runs faster, and in a larger diameter circle.

Note for geeks: In truth, the answer to this question depends on how we connect the batteries. The resistance in the circuit is dominated by the resistance of the saltwater, which may be a few hundred ohms. This is much more than the internal resistance of a 9 volt battery, which is usually around 1 or 2 ohms, or any other conductor in the circuit, which is typically a tiny fraction of an ohm. That's why, when we connect the batteries in series, the voltage is doubled, but the resistance hardly changes at all, even though there's a little extra resistance from the second battery. The net effect is that the current doubles (as determined by Ohm's law ), and the copper rod spins faster and in a larger circle. On the other hand, if we connect two batteries in parallel, the voltage remains the same (9 Volts), and the resistance hardly changes — it is still dominated by the salt water. With two batteries in parallel, the motor speed does not change.

• What happens if we fill up the container with salt water?

An electric current generally tries to take the shortest path through a conducting medium. When the current is traveling through the water between the hanging rod and the aluminum foil, it tends to travel near the surface. In particular, the current in the hanging rod leaves the rod (or enters the rod) as soon as the rod touches the water. Current does not travel much further down in the portion of the rod that is deeply immersed. If we fill up the container so that most of the hanging rod is immersed, not much of the rod will carry a current, and the part that does will be high above the magnets. Therefore not much of the rod will feel a Lorentz force. The motor should slow down.

• What makes the electric current in the wires?

Usually, current flows through a conductor because some of the electrons in conductors are only very weakly bound to their atoms. This is true of most metals. When a copper wire is connected between the negative and positive terminals of a battery, the electrons in the wire are repelled from the negatively charged terminal of the battery (two charges of the same sign repel each other) and attracted to the positively charged terminal of the battery (two charges of opposite sign attract each other). Consequently electrons move from the negative terminal, through the wire, to the positive terminal. This flow of electrons is the electric current.

There is one sticky point. By convention, the direction of the standard electric current is the direction of flow of positive charges. Since electrons are negatively charged, the direction of the standard current is defined to be opposite the direction of the movement of the electrons. The definition of the positive and negative charge was made before scientists actually knew what the charge carrier was in conductors. Once they discovered it was the electron that moved inside a conductor, and that the electron was negatively charged, it was too late to change. Nowadays, this secret convention, and others like it, helps provide job security to physicists and engineers.

• What makes the electric current in the water?

This current is much more complicated than the current in the copper wires. In truth, free electrons do not flow through the water. Nonetheless, the electric current can travel through the water even without a flow of electrons. All we need is for electrons to be taken away from the copper wire and surrendered to the aluminum foil (or vice versa, depending on how the battery is connected). In a saltwater solution, table salt (a.k.a. sodium chloride — NaCl) dissolves into ions Na + (a Sodium atom with an electron removed) and Cl - (a Chlorine atom with an extra electron attached). In addition, a small fraction of the water molecules also disassociate into ions: H + and OH - . In our Faraday motor, the excess electrons in the copper rod combine with H + ions in solution to make neutral hydrogen gas. When we connect the motor we can start to see hydrogen bubbles form on the copper rod. At the aluminum foil, some chlorine ions Cl- surrender their extra electrons to the positively charged alumium and form neutral chlorine gas, which will also form bubbles. The left over Na+ ions combine with the left over OH- ions to form neutral Sodium Hydroxide (NaOH) in solution. At this point, more water molecules can disassociate and the process can continue until all the sodium and chlorine ions are used up. The net effect is that electrons are taken away from the copper rod and delivered to the aluminum foil, just as if they flowed from one to the other.

• Why do bubbles form on the aluminum foil and the copper rod?

Chlorine gas is being formed at the aluminum foil (assuming it is connected to the positive terminal of the battery) and hydrogen gas is being formed at the copper rod. See the discussion above on how electric current flows in saltwater.

troubleshooting

If the motor is not working, the first thing to check is all the electrical connections. The connections at the paper clips are especially prone to disruption from oil or grime and may need to be cleaned with alcohol. Try to use new paper clips, and sand or file the interior surfaces if necessary. Check the resistance with an ohmmeter if you have one. If neither the aluminum foil nor the hanging copper rod are producing bubbles, a connection is broken somewhere.

The electrical connections in the water are also a bit unreliable. As gas bubbles form on the aluminum foil and the copper rod, they can disrupt the connection. Periodically stirring the water or tapping the copper rod on the side of the container to dislodge bubbles may help. Use several layers of aluminum foil to ensure a large surface area.

If the circuit is not complete and you suspect the connection at the paper clips, you might try replacing the paper clips with several strands of fine copper wire. You can tie or solder the wire on tightly at both ends to make a good connection, but it will still be flexible enough to allow the hanging copper rod to revolve freely.

If the magnet stack is too short and does not reach up to the bottom of the hanging wire, the motor will not work. In this case, the wire is hanging along the axis through the magnets, and the current is parallel to the magnetic field lines above the magnet, so there is no Lorentz force. The wire should hang down beside the magnets.

If the container is too full of salt water, the motor may not work. The water should be deep enough to make good connection with the hanging copper rod, but it should not be much above the top of the magnets.

teaching notes

The Faraday motor works best after students have seen and understood electromagnets and can appreciate the interaction between a magnet and a current in a wire. Check out Basic Electromagnets for some ideas. The lesson Classroom Rail Gun also demonstrates the Lorentz force in a very simple way that helps prepare students to figure out the operation of more complex motors. More precise visualization of the Lorentz force can be achieved if the students already know about magnetic field lines. See Iron and Magnets for an introductory lesson.

To initiate more discussion about where the current flows through the water, have the students start with a minimum amount of saltwater to get the motor running, and then slowly add more saltwater. When the water level is well above the top of the magnets, the copper rod should quit moving, even though bubbles are still forming on the rod near the surface of the water. (If you can't easily see bubbles forming on the copper rod, make sure the negative terminal of the battery is connected to the copper rod.) With bubbles forming near the surface of the water, but not further down on the copper rod, students will start to see that the water is only interacting with the current near the surface. See the discussion above in "questions to ponder" for more details. Siphon off some of the water to get the motor running again.

For the teacher who wants to get into the chemistry of saltwater electrolysis, one good way to introduce the topic is to have the students start with pure tap water and slowly add salt. The motor will not work with pure tap water; there aren't enough ions in tap water to support a significant current. Once enough salt has been added to start the electrodes bubbling and the motor running, a discussion on  how electric current flows through saltwater can ensue (see "questions to ponder" above).

To jumpstart a discussion on basic electronics of batteries and circuits, including series and parallel connections, just have the students replace the 9 V battery with two 9 V batteries in series and watch what happens. The electrodes will start bubbling more vigorously, and the rod will start moving faster through the water. Have the students measure the time it takes for a revolution and estimate the diameter of the circle to calculate the speed.

more resources

John Jenkins has compiled a beautiful visual history of motors showing a number of early motors, including several versions of Faraday's design, at http://www.sparkmuseum.com/MOTORS.HTM .

The folks at the National High Magnetic Field Lab have put together a Java demo of Faraday's motor so that you can do the experiment without ever getting your hands dirty.

author's suggestions

Related lessons, related curricula.

An excursion into particle physics and cosmology for non-science students

Distributed with an MIT license.

QS&BB Quarks, Spacetime, and the Big Bang

A little bit of faraday, his day job, missing in action, faraday’s health, what to remember from lesson 11, goals of this lesson:.

With pencil in hand, young Michael faithfully attended the lectures in the gallery, wrote out and bound them, and presumptively sent them to Davy. So imagine Faraday’s astonishment when one day a summons arrived for him to visit the Great Man who had fired one of his laboratory assistants for fighting and out of the blue, offered the job to Michael. His apprenticeship had ended, he was at loose ends, and so the timing was remarkably fortuitous.

He accepted and after a short introduction in the Laboratory to his amazement he was bundled up with Davy’s wife for a year and a half scientific and educational tour throughout Europe as Davy’s “philosophical assistant.” Faraday had never been more than a dozen miles from London and perched atop Lady Davy’s carriage (yes, he was made to ride on top of her coach!), the city boy delighted in letters home at the French countryside. The little scientific entourage embarked from Plymouth in October of 1813. Although the 20 year-long war with France was still raging the Great Man carried special credentials from Napoleon them to travel through enemy territory. And so, in spite of grumbling from London’s conservative press, Davy pressed forward with safe passage to Paris, then to Montpelier, Genoa, Florence, Rome, Naples, Geneva, Munich, and dozens of other towns in between. During their trip, Napoleon’s army was defeated, the Emperor was exiled, escaped, and hostilities renewed. These ominous events led them to cut their trip short, avoid France on their return to England in April of 1815.

This excellent European adventure was Faraday’s alternative college education—a continuous “study abroad” experience which brought him into direct contact with all of the scientific luminaries on the continent, some of who he corresponded with for years. Throughout, Davy did experiments with Faraday’s assistance. While exhilarating, this experience also made him very aware of his low station in life and how he appeared to others. To make matters worse, Lady Davy’s self-appointed role seemed to be the reinforcement of their apparent class distinction which led to many despondent letters home about ill treatment at her hands. Faraday was equal parts gratified for the education and miserable. He wasn’t just Davy’s scientific assistant but also expected to be Dir Humphrey’s valet. Faraday determined to change his manner and his speech and when they returned took elocution lessons and joined reading groups which he attended his whole life. “Self-made man” seems a label designed for Michael Faraday. With their return, Michael spent the rest of his life working within the Royal Institution, eventually with his wife in provided apartments. Davy later commented that his most famous discovery was “Michael Faraday,” but the good feelings didn’t last, as much later the temperamental Davy wrongly accused Faraday of plagiarism and unsuccessfully tried to block his election to the Royal Academy of Science…a sorry chapter in an otherwise heart-warming relationship.

Davy quickly came to totally depend on Faraday. He chafed under the assistant’s role, but broke through—by 1820 he started his own researches and naturally took up electrolysis as a study and methodically characterized both his procedures and his results. It is to him that we owe the terms “ion” and “electrode” among others.

While an extraordinary experimenter—imaginative as well as skillful, he was notoriously mathematically illiterate. He knew it, everyone knew it. Yet without any formal training, his contributions were often guided by a natural and highly developed mathematical intuition. He “thought” mathematically, he just couldn’t express his ideas in that language. Later when James Clerk Maxwell codified his work in sophisticated mathematical form, he marveled at Faraday’s intuitive and pictorial sense of the phenomena. In fact, arguably it was precisely his lack of formal training that freed him to make heretical suggestions which were quite outside of the standard wisdom…and which were often right. As his fame grew, it didn’t immunize him from scathing criticism from his more sophisticated colleagues who would object on grounds that he was out of his league. What these colleagues couldn’t appreciate was that not only was Faraday out of his league—he’d invented a whole new sport: Michael Faraday and James Clerk Maxwell were the first modern physicists.

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Faraday’s Experiments in Electricity and Magnetism

By the time Faraday was working on his own, he knew all of chemistry. Davy had been a pioneer and was devoted to an atomistic-molecular view which rubbed off on Faraday who tended to think in terms of particulate matter all of his working life. His skills as an analytic chemist were second to none and he was in considerable demand for industrial consultation, fitting right into the goals of the Royal Institution. He created compounds of chlorine (discovered by Davy) and carbon, he isolated Benzine (and other organic molecules), liquefied chlorine, and discovered paramagnetism. He made important advances in alloying of steel. He was the go-to man in Britain for industrial chemistry innovation. Our concern is with this research into electricity and magnetism. Let’s consider each of his major discoveries in their historical order.

Oersted’s results in 1820 electrified the Davy-Faraday laboratory. Their lab was proficient in electro-chemistry and so they must have had many of the materials required in order to repeat Oersted’s experiment, and they did in great detail. It was Faraday who imagined that Oersted’s compass demonstrating a circular relationship around a current-carrying wire might imply that magnets might themselves feel circular force around a wire. He had the clever idea to construct such a device, making use of the fact that mercury is a good conductor of electricity, while still being a fluid.

Look at the left side of the figure above. The beaker of mercury has a bar magnet attached on a swivel at the bottom and at the top of the pool of liquid, a wire just breaks the surface. The wire running off the bottom to the left is attached to a battery and the vertical wire (ignoring the right hand part of the picture) is attached to the other terminal of the battery. When current flows through the mercury and the wire, the magnet swivels around its base in a circle around the upper wire. That’s a different demonstration of what Oersted observed – that a magnetic disturbance surrounds a current. Here the magnet swinging around the wire is experiencing that disturbance.

The right hand picture shows is sort of the opposite. The magnet is fixed and has its own magnetic disturbance and the current-carrying wire is free to swivel…mechanical motion is induced in the current, where before mechanical motion is induced in the magnet. In each case (left and right) the circuit is completed through the mercury and the vertical wires.

Faraday connected the two experiments together as a show-and-tell stunt demonstrating the complimentary aspects of the same phenomenon: electrical energy is converted into mechanical motion, which is…the first motor. When you flip the switch on a wall and your garage door goes up, that’s a motor at work. The opposite of a motor is a generator, in which you convert mechanical energy into electrical energy. Your car has a generator that takes the mechanical energy of the engine and converts it into electrical energy to charge your battery.

Electrical energy can induce circular mechanical motion in a circuit.

Faraday knew that this was a significant discovery. In his notebook he wrote, “Very satisfactory, but make a more sensible apparatus.” But his 14 year old brother-in-law, who was in the lab with Faraday’s wife, Sarah noted later that they all danced around the apparatus and then went to the circus to celebrate. (He even prepared small hand-held versions of the Faraday Motor that he gave to colleagues for their amusement.) Faraday had none of the “Newton upbringing” and so his mind created different pictures. This idea of circular forces didn’t fit into a Newtonian force-world and in this regard, Faraday was completely on his own.

In 1821, young Faraday was asked to write an article which would summarize the all of the known electrical and magnetic phenomena. By this point, he was an extraordinarily careful experimenter and exceedingly clever with his notebooks, inventing an indexing system that he’d use his entire career. Instead of just reviewing the literature, he decided to repeat all of the experiments that had ever been done on electricity which for a genius like Faraday, led him into new territory.

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By 1825 Faraday was the director of the Royal Institute and inherited fund raising and financial affairs which were a considerable burden, as the place was nearly broke. Its purpose was originally to assist British industry with solutions which could be sold or which would increase efficiency in the nation’s factories. That contrasted with Faraday’s own personal desire to continue to do fundamental research, undirected by practical application. He found time to do so, but it was less than he would have liked. It was not until 1831—the year that Davy died—that he was able to return to basic research in electricity and magnetism. But he was always working on matters of public good and industrial progress. Basic research was inserted when he had time.

But one thing he had time for was pay-back. Remember his good fortune in life had come with an opportunity of a chance public lecture. Faraday devoted himself, throughout his life, as an engaging and entertaining presenter of science to the public. As director, he instituted a nearly weekly series on Fridays—always exactly one hour—and he created a Christmas series for children. The Royal Institution Christmas Lectures have been given every year (except during WWII) from a virtual “who’s who” of British scientists. Look at that overflow crowd in one of his last lectures below. Michael Faraday was the world’s first “Mr Wizard.”

By 1831, he managed to clear his research decks sufficiently to take on a problem that had plagued him, as well as others. Clearly there were two ways to produce electricity: one could use friction—the silk and fur rubbed on glass and amber (your socks on the carpet) or use chemistry – a battery. And, Oersted and Ampère had shown that electricity – in the form of a current – could produce magnetism. So surely magnetism should be able to produce electricity?

Faraday went into a furious series of experiments trying all manner of materials and conductors which mostly consisted of trying to take adjacent circuits and get one to cause a current in another. His inspiration came when he took two long wires and wrapped them individually in paper and then wove them together around a core of a circular iron ring. One of his cores is shown at the right.

The paper insulated the wires from touching, but they were all very close to one another. He hooked one set to a battery and looped the other circuit over a sensitive magnetic needle as shown in the figure below. If the needle moved when the current flowed in the first circuit, then it would have been induced by the interwound, but insulated wires. Multiple tries didn’t succeed until he noticed that the needle moved when the circuit was closed and then when it opened…and was stationary when the current just flowed. That was the key which everyone had missed, including after seven years of effort by Faraday: currents don’t induce magnetism, but changing currents do!

Subsequently, he found another demonstration of a similar sort, but more directly and forcefully a magnet inducing electricity. In the figure below is just a loop of wire connected to a Galvanometer. No battery. No currents. Pointed at the loop is a bar magnet. That’s it. Hold the magnet still, nothing happens. But, move the magnet toward or away from the loop and a current flows in it! Here, the changing magnetic influence is caused by a mechanical motion of the magnet. Current is created by a changing magnet, which is the principle behind a Generator. Keep this little experiment in mind.

The ability for current to flow seems to be inside of the wire and by changing a magnetic field in the vicinity of the wire, that current is induced to flow. This phenomenon is called Electrical Induction and it’s the principle behind all generators—creating current out of magnetic motion—and motors, its inverse—creating motion out of currents.

A changing magnetic influence creates a current.

What’s responsible for all of these various phenomena? Faraday had the standard repugnance for Action at a Distance, and knew that that wasn’t an explanation of anything anyway. He wasn’t so bound to the idea as were his classically trained colleagues, and so he thought about it in his own, fresh mind.

Faraday announced his discovery to the world at a meeting of the British Royal Society on November 24, 1831. That led to a priority struggle, as the publication of the effect was in early 1832, by which time the effect had been repeated in France and Italy…and where popular press reported that Faraday had confirmed the effect, rather than discovered it. He never again announced a discovery before formally publishing it in an international journal. The French and Italian scientists all acknowledged his priority and so trouble was averted. By now “Professor” Faraday – the uneducated printers apprentice – was world-renown and what he said and did mattered.

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Faraday handled mercury and other dangerous materials as a matter of course. In his middle age he suffered a serious lack of memory and bouts of dizziness that took him out of action from about 1839 until 1845. It must have been terrifying. He was forced into months of seclusion and was absent from research only giving a few public lectures in the 1840s. Speculation is that he had poisoned himself. Can you imagine someone as energetic and inspired as Faraday, unable to work? Neither could Sarah, who enforced strict social access to her husband throughout his convalescence. He eventually recovered and resumed his activities. The challenge that seemed to energize him was his evolving view of space and the vacuum.

Look carefully at the figure just above and the figure to the right, the proverbial 1000-words’-worth kind of pictures. The first is from Faraday’s notebook, and so a sketch made by him sometime in the early 1830’s. The second is a photograph from our lecture hall. What you see is a bar magnet surrounded by little bits of iron filings, each a little magnet of its own. By tapping the surface one frees them from any friction with the surface and they respond to an unseen presence—what Faraday called “lines of force.”

One really cannot help but be mesmerized by this picture when you think about what it suggests. At first Faraday used the image of “lines of force” as a visualization…but by 1831 (in his diary) and 1845 in public and in print, he began to speak of the reality of what he coined a “field.” While a compass points north, responding to an apparently invisible quality, these pictures revealed to Faraday that there’s something there, hidden from view. Like a ghost materializing out of thin air in a Halloween cartoon, these lines of force reveal themselves by their spooky influence on the iron filings.

Faraday, like everyone, had trouble with Newton’s action at a distance – that one body could reach out and influence another body with nothing in-between. But the scientific community – especially those in Newton’s Britain – and come to peace with instantaneous, Action at a Distance.

But his simple experiment shows that there’s something there . Faraday played with this idea for years but slowly became committed to the reality of the lines of force – that empty space was not empty at all, but full of this almost material substance that seemed to propagate magnetic influence from one place to another. Faraday was aware that these were not going to be popular notions. First these lines of force were not Newtonian in character – they curved . They were circular . Maybe even worse: they seemed to endow space itself with something to do . In the Newtonian way of thinking, all space did was establish “place.” It just defined separations between objects and staked out occupied regions. But Faraday’s lines of force, if real, filled all of space. The effects of magnetism required space-filling lines of force. Or so his ideas went. But he didn’t publish these ideas.

Instead, for years he amassed his evidence. Look at figure below, again from his notebooks. Here we see the cross section of a wire (top) and two wires (bottom) all carrying currents. Iron filings were sprinkled on the sheet of paper punctured by the wires and again, by their orientation and arrangements, the filings signal the presence of magnetic lines of force. From the Oersted experiment, he knew that a current creates a magnetic effect and here he’s shown it to be of the same sort of disturbance as from a bar magnet. It was time to come clean.

Finally, in 1837 he read what was the 11th of a series of Experimental Researches in Electricity to the Royal Society and he proposed that rather than being just a mental crutch, perhaps the lines of force were real. This was a frontal assault on (British) scientific belief and the reaction was not pleasant. In particular in the audience was the young William Thomson (the future Lord Kelvin), who was disgusted with the idea. Until he worked on it. What Thomson did was to apply the mathematics of heat conduction to the “streamlines” of Faraday’s lines of force. He found that it hung together and by 1845, when he first actually met Faraday, he proposed that magnetic forces might actually affect the passage of light through materials.

Faraday set out to try to observe Thomson’s effect, obviously encouraged that someone who was of the traditional scientific establishment, and a mathematical person to boot, would take his ideas seriously. He worked feverishly without results for almost a week, until he found the effect, which is today called the Faraday Effect: the presence of a magnet affects the polarization of light in some materials.

Aha. A magnetic disturbance affecting the propagation of light…were they connected?

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Light is an undulatory phenomenon – it’s a wave. For his colleagues the idea of light propagating through a vacuum was ludicrous. There had to be something “waving” for the light beams to undulate. In the classic sense of naming something being satisfying, but not really explaining, this “something” was called the Ether …specifically, the “Luminiferous Ether” for the Ether that propagated light (there were thought to be other ethers that propagated electricity and magnetism).

The Luminiferous Ether was a strange beast: It was everywhere. It didn’t impede the motion of the Earth. It couldn’t be seen, felt, tasted, or nudged and yet it could delicately react to light which stretched and compressed it as it propagated from one place to the other. Yet, since the speed of light was known to be very fast, the ether would have to be stiffer than steel to vibrate at that rate! The idea is very strange. Too much so for Faraday whose views on space were extreme. He had no time for this unrealistic, invisible ether. Rather than imaging space to be just a big container that keeps everything from being all in the same place(!), he imagined a space that was full of electric and magnetic lines of force.

For example his induction experiment could be explained this way. Look again at the figure above of the coil and the approaching magnet. As the magnet approaches the patiently waiting, inert coil of wire, more and more lines of flux are “cut” (his word) by the wire and it’s the cutting of the “flux” (his word) that starts the current to flow. In fact, he even imagined that this magnetic flux would take time to reach the wire, so it was not instantaneous. Were a wire to be parallel to the lines of force, there would not be any current. Only when the lines of force cut a wire, would current flow.

After that public exposure, Faraday tried to be more specific in a letter to Philosophical Magazine .

“The propagation of light and therefore probably of all radiant action, occupies time; and, that a vibration of the line of force should account for the phaenomena [sic] of radiation, it is necessary that such a vibration should occupy time also…I think it is likely that I have made many mistakes in the preceding pages, for even to myself, my ideas on this point appear only as the shadow of a speculation, or as one of those impressions on the mind which are allowable for a time as guides to thought and research. He who labours in experimental inquiries knows how numerous these are, and how often their apparent fitness and beauty vanish before the progress and development of real natural truth.”

He was roundly criticized for this speculation. He chalked it up to his learned colleagues being overly cautious and hide-bound to their preconceptions. His colleagues basically indicated that Faraday was a brilliant experimenter, but out of his depth when he ventured into speculative ideas about nature and mathematics. Faraday needed a hero and we’ll meet his champion in the next chapter.

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Faraday’s health was a constant concern in his 50s and later. He might have suffered from mercury poisoning. He was terribly worried about his memory losses and found that only trips to the country and a heavily-enforced isolation from anything scientific would restore him to working form. However, he had to exit himself for a couple of years to recover from a particularly bad episode and it never quite left him alone after that.

Faraday continued to experiment and unravel a number of mysteries in both chemistry and physics. He never forgot his modest education and worked hard to perfect a speaking and demonstration ability, giving many public talks in London through his senior years.

What we take from Faraday’s work is of course the list of phenomena that he demonstrated. But, as important, or maybe even more so since other natural scientists would have come upon these same events. It was rather that mathematical intuition which when combined with his naivety about how things were “supposed” to be, that is his enduring contribution. Those lines of force, which he carefully mapped and measured in a number of electrical and magnetic configurations were the direct inspiration to arguably the most accomplished mathematical physicist apart from Newton and Einstein.

He died at the age of 73. Increasingly aware of his inability to remember and function, he resigned from the Royal Institution. His last lecture was given on a Friday and his notes bear some scorch marks where apparently they got too close to an open flame. He announced his retirement at that lecture to what must have been a stunned audience.

“It is with the deepest feeling that I address you.\ I entered the Royal Institution in March 1813, nearly forty-nine years ago, and, with exception of a comparatively short period, during which I was absent on the Continent with Sir Humphry Davy, have been with you ever since.\ During that time I have been most happy in your kindness, and in the fostering care which the Royal Institution has bestowed upon me. I am very thankful to you, and your predecessors for the unswerving encouragement and support which you have given me during that period. My life has been a happy one and all I desired. During its progress I have tried to make a fitting return for it to the Royal Institution and through it to Science.\ But the progress of years (now amounting in number to threescore and ten) having brought forth first the period of development, and then that of maturity, have ultimately produced for me that of gentle decay. This has taken place in such a manner as to render the evening of life a blessing:—for whilst increasing physical weakness occurs, a full share of health free from pain is granted with it; and whilst memory and certain other faculties of the mind diminish, my good spirits and cheerfulness do not diminish with them. Still I am not able to do as I have done. I am not competent to perform as I wish, the delightful duty of teaching in the Theatre of the Royal Institution, and I now ask you (in consideration for me) to accept my resignation of the Juvenile lectures… I may truly say, that such has been the pleasure of the occupation to me, that my regret must be greater than yours need or can be.”

He and his wife, Sarah, never had children but they were very content with one another, as evident in a letter her on one of his last trips,

“My head is full, and my heart also, but my recollection rapidly fails, even as regards the friends that are in the room with me. You will have to resume your old function of being a pillow to my mind, and a rest, a happy-making wife.”

He referred to himself as “altogether a very tottering and helpless thing, and requested a small funeral, attended by only his family. He died in 1867 and at the ceremony planned for family, friends and colleagues “came out from the shrubbery” to say goodbye.

The Times of London obituary said in part,

The Late Professor Faraday “The world of science lost on Sunday one of its most assiduous and enthusiastic members. The life of Michael Faraday had been spent from early manhood in the single pursuit of scientific discovery, and through his years extended to 73, he preserved to the end the freshness and vivacity of youth in the exposition of his favourite subjects, coupled with a measure of simplicity which youth never attains…as a man of science he was gifted with the rarest of felicity of experimenting…It was this peculiar combination which made his lectures attractive to crowded audiences in Albemarle-street for so many years, and which brought, Christmas upon Christmas, troops of young people to attend his expositions of scientific processes and scientific discovery with as much zest as is usually displayed in following lighter amusements…

Faraday was beloved around the world and the Times listed a few of his honors:

Oxford conferred on him an honorary degree…He was raised from the position of Corresponding Member to be one of the eight foreign Associates of the Academy of Sciences. He was an officer of the Legion of Honour, and Prussia and Italy decorated him with the crosses of different Orders. The Royal Society conferred on him its own medal and the Romford medal. In 1858 the Queen most graciously allotted to him a residence at Hampton Court, between which Albemarle-street where he spent the last years of his life, and where he peaceably died on Sunday…No man was ever more entirely unselfish, or more entirely beloved. Modest, truthful, candid, he had the true spirit of a philosopher and of a Christian… The cause of science would meet with fewer enemies, its discoveries would command a more ready assent, were all its votaries imbued with the humility of Michael Faraday.”

A changing magnetic influence can create an electric current, while a stationary magnetic influence cannot. This is called induction and the historical name is Faraday’s law.

This is to go along with Oersted’s discovery that an electric current creates a magnetic influence.

Mechanical energy can be derived from electrical energy and motors do that. Likewise, mechanical energy can create electrical energy and generators do that.

Michael Faraday's sample of benzene

Isolated for the first time in 1825 this hydrocarbon is now an important raw material in manufacturing dyes, explosives, rubber, phenol and therapeutic chemicals.

Date : 1825

Place made : Basement laboratory at the Ri

Alternative name : Bicarburet of hydrogen

Materials : Glass, Cork, Benzene

Measurements : Height: 146mm,  diameter: 44mm

Description

A small vial containing Faraday’s sample of benzene, a colourless liquid with a sweet smell. If you look closely you can see ‘Bicarburet of hydrogen’ scratched onto both the vial and the bottle.

Benzene is a natural hydrocarbon and a component of crude oil.  Faraday isolated this substance for the first time in 1825 while investigating an oily residue that was created as a by-product of the production of ‘portable gas’. Portable gas was created by dropping whale or fish oil into a hot furnace, compressing the gas which was created and then storing it in containers to use in lamps in private and public buildings.

Faraday was interested in the liquid which formed when the gas was pressurised. He experimented with distilling this mixture and, as he reported in a paper to the Royal Society on 16th June, he ‘succeeded in separating a new compound of carbon and hydrogen, which I may by anticipation distinguish as bi-carburet of hydrogen’.

By the mid 19th Century benzene was being manufactured on an industrial scale from coal tar. It was mainly used as a solvent for degreasing engines, but by the 20th century, it was in use for everything from aftershave lotions to part of the process of making decaffeinated coffee. The substance is now known to be toxic and is now used mainly in industrial processes to create other substances.

The structure of benzene has been the subject of much research. Many theories were put forward throughout the 19th century but it wasn’t until 1925, a century after its discovery that Kathleen Lonsdale confirmed the structure through x-ray crystallography, using photos taken at the Ri (although not from this sample).

Where can I view this?

This object is currently on display on the lower ground floor of the Royal Institution in the  Faraday Museum .

More images

More about Michael Faraday

History of science

Michael faraday's electric magnetic rotation apparatus (motor).

The first surviving Faraday apparatus, dating from 1822, demonstrates his work in magnetic rotation. Faraday used this mercury

Michael Faraday's ring-coil apparatus

Made by Faraday in his laboratory in the basement of the Royal Institution in August 1831, thus creating the first ever electric

Michael Faraday's magneto-optical apparatus

The electromagnet used by Michael Faraday in a ground-breaking experiment showing that light and glass are affected by magnetism

Michael Faraday's generator

Faraday created the first transformer in August 1831. A few months later he designed and made this simple piece of apparatus

A tour of Michael Faraday in London

A walk from the Royal Institution to Somerset House exploring Faraday's life, his intellectual network and his legacy.