Mauveine: The first synthetic dye for cloth

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Mauveine was the first synthetic dye for cloth; every color on fabric in the mid-1800s had to be extracted from something in nature, such as a berry’s juice or a beetle’s exoskeleton. The best purple dye available at the time was made from mollusc mucus, which was difficult and expensive to extract. Mauveine was a cheaper and more color-fast alternative, and at the height of the industrial revolution, William Henry Perkin‘s timing was perfect.

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Electricity and Magnetism

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Milestones in Electricity

  1. From Greek period to 18th Century: transient or ephemeral electricity in the form of sparks and shocks
  2. Invention of steady electricity: The Volta Pile in 1800s
  3. Faraday and Maxwell
  4. 1881: First International Exposition of Electricity at Paris
  5. 1893 World’s Columbian Exposition in Chicago: AC Power Generator
  6. Invention of Transistors


Development of Electricity


During prehistoric times, early humans were aware of lightning, sting rays, electric eels, and static charges in dryclimates


600 BC: The Greek philosopher Aristophanes was aware of the peculiar property of amber, which is a yellowish translucent resin. When rubbed with a piece of fur, amber developed the ability to attract small pieces of materials such a feather. For centuries this strange inexplicable peopety was thought to be unique to amber.


Thales (640-546 BC) rubbed amber (elektron in Greek) with cat fur and picked up bits of feather.


341 BC: Aristotle wrote about a fish called torpedo which gave electrical shocks and paralyzed muscles if touched.


250 BC: A Galvanic cell composed of copper nd iron immersed in wine or vinegar called the Baghdad Batter was excavated in Baghdad by Wilheim Konig in 1938 and was dated back to 250 BC.


1600 AD:

Gilbert also studied magnetism and in 1600 wrote “De magnete” which gave the first rational explanation to the mysterious ability of the compass needle to point north-south: the Earth itself was magnetic. “De Magnete” opened the era of modern physics and astronomy and started a century marked by the great achievements of Galileo, Kepler, Newton and others.

Gilbert recorded three ways to magnetize a steel needle: by touch with a loadstone; by cold drawing in a North-South direction; and by exposure for a long time to the Earth’s magnetic field while in a North-South orientation.

1600 AD: Sir William Gilbert (1544-1603), the Court Physician to Queen Elizabeth I, proved that many other substances besides amber displayed electrical properties and that have two electrical effects. When rubbed with fur, amber acquired resinous (negative) electricity; glass however, when rubbed with silk, acquired vitreous (positive) electricity. Electricity of same kind repels and of opposite kind attracts. Gilbert’s book On the Magnet and Magnetic bodies and on the great magnet the Earth published in 1600.
They did not realize that an equal amount of opposite electricity remained on the fur or silk. Dr. William Gilbert, realized that a force was created, when a piece of amber (resin) was rubbed with wool and attracted light objects. In describing this property today, we say that the amber is “electrified” or possesses and “electric charge”. These terms are derived from the Greek word “electron” meaning amber and from this, the term “electricity” was developed. It was not until the end of the 19th century that this “something” was found to consist of negative electricity, known today as electrons.


1646: Walter Charlton coined the term electricity.


1663: Otto von Guericke first published the phenomenon of static electricity snd built a machine to produce it. Also Read: The History of Electrical Machines


1729 – Conductors and Nonconductors

Stephen Gray was the first to systematically experiment with electrical conduction. Until his work in 1729 the emphasis had been on the simple generation of static charges and investigations of the static phenomena (electric shocks, plasma glows, etc.). He also first made the distinction between conduction and insulation, and discovered the action-at-a-distance phenomenon of electrostatic induction.

 1747: Ben Franklin during a thunderstoem demonstrated that lightning was an electrical discharge. The experiment was extremely hazardous, but the results were unmistakable: when he held his knuckles near the key, he could draw sparks from it. The next two who tried this extremely dangerous experiment were killed.
Watson passed an electrical charge along a two-miles long wire.


Resolutions of the International Congress of Electricians, Paris, 1881

(1) That the cgs system of electromagnetic units be adopted as the fundamental units.

(2) That the practical units, the ohm and the volt, preserve their previous definitions, 109 and 108 cgs units respectively.

(3) That the unit of resistance, the ohm, be represented by a column of mercury 1 mm² in cross-section at the temperature of 0° C.

(4) That an international commission be charged with the determination, by new experiments, of the length of the mercury column 1 mm² in cross-section at a temperature of 0° C.

(5) That the current produced by a volt in the ohm be called an ampere.

(6) That the quantity of electricity produced by a current of 1 ampere in one second be called a coulomb.

(7) That the unit of capacity be called a farad, which is defined by the condition that a coulomb in a farad raises the potential 1 volt.

The term electroscope is given to instruments which serve two primary purposes: 1) to determine if a body is electrified, and 2) to determine the nature of the electrification. An electrometer, on the other hand, is a specialized form of electroscope that includes a calibrated scale for reading the strength of the charge.


  1. Progress before the invention of Volataic Battery
  2. Invention of the Voltaic Battery
  3. Post Voltaic Battery

  1. Otto Guericke Ref 1, Ref 2, Ref 3
  2. Next

Heinrich Hertz

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Heinrich Hertz’s Wireless Experiment (1887)

Spark-Gap Transmitter


Hertz’s Experimental setup schematic diagram



Hertz Experimental Setup


EM Wave from Hertz’s experimental setup


The EM wave in 3D Animation



Hertz Experiment



The existence of electromagnetic waves was confirmed experimentally by Hertz in 1888. This experiment is based on the fact that an oscillating electric charge radiates electromagnetic waves. The energy of these waves is due to the kinetic energy of the oscillating charge.

Due to high potential difference across S1 and S2, the air in the small gap between the spheres gets ionized and provides a path for the discharge of the plates. A spark is produced between S1 and S2 and electromagnetic waves of high frequency are radiated. Hertz was able to produce electromagnetic waves of frequency about 5 × 107 Hz.

Here the plates A and B act as a capacitor having small capacitance value C and the connecting wires provide low inductance L. The high frequency oscillation of charges between the plates is given by



Our eyes are designed to detect a small portion of the electromagnetic spectrum. This part of the spectrum is called the visible light region. The visible light region ranges in wavelengths from about 380 or 400 nm to 700 or 780 nm.  In terms of frequency, this corresponds to a band in the vicinity of 430–770 THz.

Light waves travel at very high speeds and are absorbed or reflected by various objects. If all the waves are absorbed and none reach our eye then we do not see anything and the image before us appears as having the color of black. If the object reflects all wavelengths of light equally then the object appears to be the color of white. If an object on the other hand reflects light of certain wavelengths but absorbs others then the color of the object will match the wavelengths that are reflected.


Table 5.1 shows various regions of electromagnetic spectrum with source, wavelength and frequency ranges of different electromagnetic waves.


Spectrum of waves


Other areas of 19th century physics were challenged by discovery after discovery tied to improvements in technique and materials. Hitherto unknown types of radiation were detected, not directly by the human senses, but by their physical effects. Thus 1799 brought the discovery of infrared rays; 1800, ultraviolet rays; 1886, radio waves; 1895, x-rays. The apparent stability of matter itself was shattered with the discovery of radioactivity by Henri Becquerel in 1896.

The high point of this scientific turmoil was the discovery of two new types of universal forces: electricity and magnetism. Alessandro Volta’s pile, the first battery, was assembled in 1800. Flowing electricity was found to create magnetism by Hans Ørsted in 1820. Michael Faraday showed that changing magnetic fields created electricity in 1831, and thus created the basis for modern electrical power generation. Faraday also first described magnetism using the concept of a field of magnetic lines existing in definite physical relations with other forms of matter. Contemporaries viewed this field as merely a mathematical abstraction, but the later work of Maxwell and much of 20th century physics showed that fields do in fact exist as an independent material reality.

The full theory of these phenomena was worked out by James Clerk Maxwell, whose equations of 1861 and their refinement in 1865 would unify electricity and magnetism into a new theory of electromagnetism. This theoretical unity for a natural force was matched only by Newton’s work on gravitation, two centuries previously. The great physicist Ludwig Boltzmann gave some voice to the impact Maxwell’s contribution made when he quoted Goethe’s Faust: “Who was the god who wrote these lines?”

Maxwell’s equations, tested by Heinrich Hertz’s deliberate construction of equipment to produce and detect the predicted waves we now call radio, suggested the various other “rays” already discovered composed a common form as electromagnetic waves. What distinguished them was simply the wavelength between crests in an electromagnetic spectrum of radiation.

Into this ferment was born Albert Einstein in 1879, just months before Maxwell’s death. The young Einstein was captivated by Maxwell’s work. In autobiographical notes, he stated, “The most fascinating subject at the time I was a student was Maxwell’s theory.” Inspired by Maxwell’s study of light, a 16-year-old Einstein conducted his first significant gedankenexperiment (thought experiment). He imagined what it would be like to ride along such an electromagnetic wave at the same speed. Would it appear frozen, since the motion would be along its crest, like surfing along an ocean wave? The equations did not admit this possibility. More intriguingly, the theory of electromagnetism posited a fixed velocity—the speed of light—while Newton’s equations implied no such limit, instead describing the force of gravity operating with instantaneous effect.


  2. Hertz and Radio Waves Explained by High School Physics Explained
  3. PHYS 101/102 #1: Electromagnetic Waves by Cornell University — Youtube Video

Newtonian Gravity Vs General Relativity

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General relativity & Gravity by stevebd1 Youtube

Warping of space around the sun

GETTING A GRIP ON GRAVITY  Einstein’s general theory of relativity explains gravity as a distortion of space (or more precisely, spacetime) caused by the presence of matter or energy. A massive object generates a gravitational field by warping the geometry of the surrounding spacetime.

If a light ray happens to pass close to a massive object such as a star, it will be forced to bend in order to follow the curved space around it.

Notice that in the above figure, the star at position at location “Real” can only be seen at position “Observed” from the earth if the light bends as shown. If the light did not bend, you would not see the star because it will be blocked by the sun shown in the middle.

The picture above shows how the direction of light will be affected by the  curved space around the sun. Light emanating from the “Real” position will curve around the outermost fringe of the curved space around the sun, and then, once out of the curved space, will travel in a straight line to the earth. From the earth, it will appear like the star is at the “observed” position when, it actually is at the “Real” position.



Newton first computed the angle of the bending light as 0.87 arc second, Einstein in 1915 modified it to be the double of that which is 1.75 arc second. From the angle of bend, the physicists computed the weight of light.

When the sun is not anywhere close to the path between the earth and the star, you could see the star at the “Real” position because the light will travel in a straight line to the earth.

Gravitational Lensing


Gravitational lensing was first observed in 1979, but Einstein had suspected its possibility in 1912, even before his theory had been completed.

The bending of light by gravity can lead to the phenomenon of gravitational lensing, in which multiple images of the same distant astronomical object are visible in the sky.

This diagram shows how light from a distant galaxy bends around a massive object in the foreground, perhaps a neutron star or a black hole. The orange arrows show the apparent position of the background galaxy. A duplicate or multiple image can be observed from Earth. The white arrows show the path of light from the true position of the source.

Angle of the bending light

Einstein  in 1911 obtained a deflection angle of (radians) = 0.87 arc second,  which is the Newtonian value.

About four years after his first paper in 1911, Einstein had developed the General Theory of Relativity (1915) which prompted him to modify the above Newtonian value by adding the effect of curved space thus doubling the bending angle resulting in a new value of 1.75 arc seconds (1.7505395 arc second). The new result was published by Einstein on November 18, (1915) and was experimentally verified by Crommelin and Eddington during the solar eclipse expeditions of May 29, 1919.

Any large mass distorts the geometry of space around it (Note the word “around”), for instance making parallel light rays diverge or converge. One consequence, described by Einstein’s general theory of relativity is that objects behind a body such as the Sun may look magnified or distorted as the optical path of light goes through the region of warped space.

The bending of light in gravitational fields is much better explained by Snell’s law of refraction (see Fig. 1) which was experimentally established by Willebrod Snell and theoretically by René Descartes over three hundred years ago.

Bending Light
The first prediction put to test was the apparent bending of light as it passes near a massive body. This effect was conclusively observed during the solar eclipse of 1919, when the Sun was silhouetted against the Hyades star cluster, for which the positi ons were well known.

Sir Arthur Eddington stationed himself on an island off the western coast of Africa and sent another group of British scientists to Brazil. Their measurements of several of the stars in the cluster showed that the light from these stars was indeed bent as it grazed the Sun, by the exact amount of Einstein’s predictions. Einstein became a celebrity overnight when the results were announced.

The apparent displacement of light results from the warping of space in the vicinity of the massive object through which light travels. The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement o f light as gravitational lensing.

Important Historical Anecdote: The solar eclipse of 1919 

Albert Einstein’s prediction of the bending of light by the gravity of the Sun, one of the components of his general theory of relativity, can be tested during a solar eclipse, when stars with apparent position near the sun become visible.

Two expeditions were made to measure positions of stars during this eclipse. The first was led by Sir Frank Watson Dyson and Sir Arthur Eddington to the island of Principe (off the west coast of Africa), the second by Andrew Claude de la Cherois Crommelin and Charles Davidson to Sobral in Brazil.

The expedition to observe the eclipse proved to be one of those infrequent, but recurring, moments when astronomical observations have overthrown the foundations of physics. In this case it helped replace Newton’s Law of Gravity with Einstein’s theory of General Relativity as the generally accepted fundamental theory of gravity.

Following were the three possibilities: There might be no deflection at all; that is to say, light might not be subject to gravitation. There might be a `half-deflection’, signifying that light was subject to gravitation, as Newton had suggested, and obeyed the simple Newtonian law. Or there might be a `full deflection’, confirming Einstein’s instead of Newton’s law.

The nice thing about using mass instead of mass is that mass is a property that all observers agree on, whereas mass is not. There aren’t that many properties of an object that are like this.  Take the speed of an object; different observers won’t agree on what it is.  For instance, there goes a car; how fast is it moving? Well, from your point of view, standing by the road, perhaps it is moving at 80 kilometers per hour.  But from the point of view of the car’s driver, the car isn’t moving at all; you’removing.  And from the point of view of someone in a car going the other direction, the first car may be moving at, say, 150 kilometers per hour.  The bottom line?  Speed is a relative quantity; you cannot ask, what is the speed of the car, because it has no answer.  Instead you must ask, what is the object’s speed relative to a particular observer.  Every observer has an equal right to make the measurement, but different observers will get different answers.  Galileo’s principle of relativity (long before Einstein’s principle of relativity, which involved adjusting Galileo’s principle)  already incorporated this idea.

This dependence on the observer also applies to energy, and to momentum.  And it applies to relativistic mass.  That’s because relativistic mass is simply the same as energy, divided by a constant — namely, c² — and so, if you define mass to be “relativistic mass“, then different observers disagree about an object’s mass m, though all agree that E=mc².

But rest mass, or, as I would call it, “mass“, does not depend on the observer, which is why it is also called invariant mass.  All observers agree on an object’s mass m, with this definition.  And all observers agree that if you were stationary with respect to the object, you would measure its energy to be mc², and otherwise you would measure its energy to be larger.[3]

Newton’s equations still differed from Maxwell’s equations in that they implied instantaneous action, that is, infinite velocities. Special relativity had decisively shown that the fastest velocity was that of light, thus limited the speed at which even gravity could influence matter.

E equals m cee squared

One of the consequences of Einstein’s theory is that mass and energy, rather than subject to separate and independent conservation laws, are conserved together and are therefore at some fundamental level equivalent. This famous equivalence of mass and energy is expressed in the equation known across the world: E=mc2. The speed of light links small amounts of mass to enormous amounts of potential energy. Originally thought to be only of academic interest, this conversion was later carried out through the mechanism of the nuclear fission chain reaction. The energy released by the two atomic bombs dropped by the United States at the end of World War II, which each incinerated a city, was the equivalent of less than one gram of mass.




Issac Newton

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  1. Gravity
  2. Newtonian gravity vs General relativity

The Solar System Master.gif

From Here

The Solar System 01


When you compute weight (gravitational mass) of an apple, you know that the earth is pulling it from all over the place. But, you should imagine that it is the center of the earth that is pulling it. This is true when you are computing the gravitational force of any spherical object such as earth – the distance between the center of the earth and the center of the apple shown here is the distance between them.

Mass and Weight

Imagine lifting a 50 kg crate across a smooth floor on earth as shown on the left.

On the Earth the weight of the crate will be 50×10 = 500 N

Gravity changes planet to planet in our solar system.

Now imagine taking the crate to the Moon and lifting it up there. Its mass is still 50 kg but the Moon’s gravitational pull is only about 1/6 of the Earth’s – in other words about 1.6 N/kg. (The Moon has less gravity because it is smaller than the Earth.) This means that the weight of our crate on the Moon will be 50×1.6 = 80 N and so it will be much easier to lift up.

Some examples of other masses are shown in the table.

On other planets the strength of the gravitational field and the acceleration in free fall is different from that on the Earth and so our crate would weigh different amounts if taken to these planets. The table below gives you some weights of our 50 kg crate on other planets.

(Remember that its MASS is the same everywhere including in deep space or in orbit round any planet where it would be weightless!)

Note that larger the planet, more the strength of the gravitational pull on objects towards its center and therefore, more the weight. Jupiter is the largest, therefore, the weight of the 50KG crate is highest there.

It’s interesting to look at the weights of our crate on Earth and on Saturn or Uranus. They are almost the same. That means if you were to go to Saturn or Uranus you would weigh just about the same as you do here. However on Pluto you would be lighter than on the Moon.

What do you think that means about astronauts’ athletic records on Pluto?

Astronauts liked walking on the Moon. They were able to take giant steps because they didn’t weigh as much there. If you were on the Moon you would weigh less than what you do here on the Earth. That is why the astronauts would really like walking on Pluto because they will get a lot lighter because of least gravitational pull, and cover lot more ground compared to other planers with same effort.

On the surface of our Sun the gravity pull is so strong that our crate would weigh an enormous 13 700 N!

Newton’s shell theorem

            • Newton showed that the gravitational effect of a spherically symmetric body is the same as it would be if all its mass were located at its centre (provided that you are outside the body). Planets and stars are nearly spherically symmetric, so one can calculate their gravitational effects using separations from their centres. To prove this requires some mathematics, so we do that in

          this separate file

The Inverse Square Law

inverse squares law

Newtons law of Universal Gravitation.09

Gravitational field strength within the Earth




Free falling Object

See Here for small g

Later in the 1670’s, Newton became very interested in theology. He studied Hebrew scholarship and ancient and modern theologians at great length, and became convinced that Christianity had departed from the original teachings of Christ. He felt unable to accept the current beliefs of the Church of England, which was unfortunate because he was required as a Fellow of Trinity College to take holy orders.

Happily, the Church of England was more flexible than Galileo had found the Catholic Church in these matters, and King Charles II issued a royal decree excusing Newton from the necessity of taking holy orders! Actually, to prevent this being a wide precedent, the decree specified that, in perpetuity, the Lucasian professor need not take holy orders. (The current Lucasian professor is Stephen Hawking.)


Gravitational force acts on all bodies in proportion to their masses. Why, then does not a heavy body fall faster than a light body?

The reason that a heavy body doesn’t fall faster than a light body is because the greater
gravitational force on the heavier body (its weight), acts on a correspondingly greater
mass (inertia).

FHeavy = mHeavy * a
FLight = mLight * a

The ratio of gravitational force to mass is the same for every body – hence
all bodies in free fall accelerate equally. Since  mHeavy mLight ,    FHeavy  has to be heavier than   FLight    so that “a” remains the same for both objects.

And it’s true not just near the Earth, but anywhere.

Michael Faraday

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See Faraday Experiment: From The Wonders of Electricity & Magnetism – Sept 2005 by Prof Walter Lewin [45 to 50 minutes]
Demo of Electric generator [Mins 52:45 to 57:50]

Faraday Experiment Simulator (Click on “5” at bottom right of the simulator)

Michael Faraday, coming from a poor family, received no formal education and worked as an errand boy. In the class-based English society of the time, Faraday had serious trouble fending for himself. After years of hard graft, he got a job of Lab Assistant at Humphry Davy’s Lab at the Royal Institution of Great Britain.

In early part of 1800, magnetism and electricity were two different things. Magnetism meant a strange looking metallic bar that could pull pins, clips, and other metallic stuff towards it. Electricity meant a wire connected to an ugly liquid-filled box called battery. These two “things” were disjointed – there was no connection in between.

In 1831 Faraday demonstrated that when a magnet is moved past a wire, it creates an electric current in the wire. That was the first experiment from where you got electricity not from a battery but from a moving magnet. This opened a new frontier of science and the rest is history. This particular discovery formed the basis of the electricity generator or dynamo that are used today.

Following this discovery, Royal Institution of Great Britain conferred on him the highest honor and made him a fellow. After that ceremony Faraday showed the experimental set up to British PM Robert Peel.

After seeing the demonstration, he asked Faraday ‘But, after all, what use is it?’.

Faraday replied, “I know not, but I wager that one day your government will tax it.”

Faraday’s experiment showed that you can induce current in a closed wire loop by mpving a magnet into it. But that current is feeble and stops as soon as you stop moving the magnet. You cannot do any practical work with that current.

Now, if you want to light a 100 Watt bulb in a Lab, you need to put thouands of loops around a core and then move it manually by rorating it with a handle very fast within a very strong magnet (same as moving magnet towards wire).

Which means that you have to put in energy — here manual — to move the coil to induce meaningful electrical current to light a bulb.

If you want to generate electricity on a big scale you need energy sources such as coal, or oil or nucluer energy.

Light bulbs, TVs  consume energy. This energy consumption is expressed in Watts named after james Watts.

Demo of Electric generator [Mins 52:45 to 57:50]

Note: Albert Einstein kept a picture of Faraday on his study wall at Princeton, alongside pictures of Isaac Newton and James Clerk Maxwell.

Hans Christian Ørsted

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From The Wonders of Electricity & Magnetism – Sept 2005 by Prof Walter Lewin [42 to 45 minutes]

suspended bar magnet

Figure 1. A  compass needle is really a very small magnet. You can make a compass with a bar magnet by hanging it with a piece of paper like this.

north pole of a magnet pointed toward a compass

Figure 2. When a magnet is pointed to the compass needle, the needle moves.

Image result for oersted experiment


Figure 3. Oerstead achieved the same result by replacing the bar magnet of Figure 2 with a piece of wire connected to a battery. This proves that an electric circuit behaves the same way to a compass as a bar magnet does.

Stick your thumb out on your right hand, and imagine holding the wire with your thumb pointing in the direction that current is flowing (opposite to electron flow). As your fingers curl around the wire, so are the magnetic field lines circling the conductor.

experiment to show effect of an electromagnet on a compass


Oersted experimented with  a compass, which has magnetic poles to show you which direction you are facing.

He had put the compass over a closed current loop connected to a DC battery. Then, by using a switch, he turned the circuit ON and OFF.

As soon as he turned the switch ON from the OFF state, the currect went through the wire and he was able to cause the compass needle to move.

As soon as he turned off the switch, the compas needles went back to their original position.

So he was able to demonstrate that the magnet responds to the flow of current.

He concluded that when the current was going throu ght wire, the wire became magnetic. The physicists would say the the current creates a magnetic field.

In other words, moving electric charges or electrons, creates a magnetic field. That is what Oersted showed.

Now comes the key question:

If moving electrons can create a magnetic field, can a moving magnet create an electric current?

The answer was given by Michael Faraday in 1831. The answer is Yes.  The demo of faraday’s experiment is given during the 46th to 50th minute of the lecture.

When Faraday made this discovery, a reporter asked him if this discovery will be of any practical use? Faraday answered: Some day you will tax it.

From Manual Power To Electricity

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The Cotton Manufacture to Modern factory