Tuesday, December 6, 2016

Determination of The Speed of Light

Great Ole Chstensen Roemer
Before the seventeenth century, it was generally thought that light is transmitted instantaneously.  This was supported by the observation that there is no noticeable lag in the position of the Earth's shadow on the Moon during a lunar eclipse, which would otherwise be expected if c were finite.  Nowadays, we know that light moves just too quickly for the lag to be noticeable.  Galileo doubted that light's speed is infinite, and he devised an experiment to measure that speed by manually covering and uncovering lanterns that were spaced a few miles apart.  We don't know if he ever attempted the experiment, but again c is too high for such a method to give an even remotely accurate answer.

The first successful measurement of c was made by Olaus Roemer in 1676.  He noticed that, depending on the Earth–Sun–Jupiter geometry, there could be a difference of up to 1000 seconds between the predicted times of the eclipses of Jupiter's moons, and the actual times that these eclipses were observed.  He correctly surmised that this is due to the varying length of time it takes for light to travel from Jupiter to Earth as the distance between these two planets varies.  He obtained a value of c equivalent to 214,000 km/s, which was very approximate because planetary distances were not accurately known at that time.

In 1728 James Bradley made another estimate by observing stellar aberration, being the apparent displacement of stars due to the motion of the Earth around the Sun.  He observed a star in Draco and found that its apparent position changed throughout the year.  All stellar positions are affected equally in this way.  (This distinguishes stellar aberration from parallax, which is greater for nearby stars than it is for distant stars.)  To understand aberration, a useful analogy is to imagine the effect of your motion on the angle at which rain falls past you, as you run through it.  If you stand still in the rain when there is no wind, it falls vertically on your head.  If you run through the rain, it comes at you at an angle, and hits you on the front.  Bradley measured this angle for starlight, and knowing the speed of the Earth around the Sun, he found a value for the speed of light of 301,000 km/s.

Determination of The Speed of Light
The first measurement of c that didn't make use of the heavens was by Armand Fizeau in 1849.  He used a beam of light reflected from a mirror 8 km away.  The beam was aimed at the teeth of a rapidly spinning wheel.  The speed of the wheel was increased until its motion was such that the light's two-way passage coincided with a movement of the wheel's circumference by one tooth.  This gave a value for c of 315,000 km/s.  Leon Foucault improved on this result a year later using rotating mirrors, which gave the much more accurate value of 298,000 km/s.  His technique was good enough to confirm that light travels slower in water than in air.

After Maxwell published his theory of electromagnetism, it became possible to calculate the speed of light indirectly by instead measuring the magnetic permeability and electric permittivity of free space.  This was first done by Weber and Kohlrausch in 1857.  In 1907 Rosa and Dorsey obtained 299,788 km/s in this way.  It was the most accurate value at that time.

Determination of The Speed of Light
Many other methods were subsequently employed to further improve the accuracy of the measurement of c, so that it soon became necessary to correct for the refractive index of air since c is light's speed in a vacuum.  In 1958 Froome obtained a value of 299,792.5 km/s using a microwave interferometer and a Kerr cell shutter.  After 1970 the development of lasers with very high spectral stability and accurate caesium clocks made even better measurements possible.  Up until then, the changing definition of the metre had always stayed ahead of the accuracy in measurements of the speed of light.  But by 1970 the point had been reached where the speed of light was known to within an error of plus or minus 1 m/s.  It became more practical to fix the value of c in the definition of the metre and use atomic clocks and lasers to measure accurate distances instead.  Nowadays, the speed of light in vacuum is defined to have an exact fixed value when given in standard units.  Since 1983 the metre has been defined by international agreement as the distance travelled by light in vacuum during a time interval of 1/299,792,458 of a second.  This makes the speed of light exactly 299,792.458 km/s.  (Also, because the inch is now defined as 2.54 centimetres, the speed of light also has an exact value in imperial units.)  This definition only makes sense because the speed of light in vacuum is measured to have the same value by all observers; a fact which is subject to experimental verification (see relativity FAQ article Is the speed of light constant?).  Experiments are still needed to measure the speed of light in media such as air and water.


This table gives some of the best measurements according to Froome and Essen:


DateAuthorMethodResult (km/s)Error
1676Olaus RoemerJupiter's satellites214,000
1726James BradleyStellar Aberration301,000
1849Armand FizeauToothed Wheel315,000
1862Leon FoucaultRotating Mirror298,000+-500
1879Albert MichelsonRotating Mirror299,910+-50
1907Rosa, DorsayElectromagnetic constants299,788+-30
1926Albert MichelsonRotating Mirror299,796+-4
1947Essen, Gorden-SmithCavity Resonator299,792+-3
1958K. D. FroomeRadio Interferometer299,792.5+-0.1
1973Evanson et alLasers299,792.4574+-0.001
1983Adopted Value299,792.458

Sources of information:

Twentieth Century Physics, Vol 2, IOP/AIP press.
Hutchinson Science Library.
The Velocity of Light and Radio Waves, Froome and Essen.

Monday, December 5, 2016

Biography of Jayalalitha

 Jayalalitha
Jayalalithaa Jayaraman, was an Indian politician who served five terms as Chief Minister of Tamil Nadu, from 1991 to 1996, in 2001, from 2002 to 2006, from 2011 to 2014, and finally from 2015 to 2016. Wikipedia
BornFebruary 24, 1948, Melukote
DiedDecember 5, 2016
OfficeChief Minister of Tamil Nadu since 2016
Previous officesChief Minister of Tamil Nadu (2015–2016), more

Growing up, it was clear that Jayalalithaa never experienced the same 'normal' childhood as her friends. Vaasanthi provides one example of this in a chat between two friends.
Jayalalithaa often told Srimathi that she did not like the film-world atmosphere, and that the men there were crude and stared at her lustfully. ‘Jaya would say, ‘‘When I go home these rascals will be sitting there. I get so annoyed seeing them – all kinds of men, tall, short, dark, fair, thin and fat and oily! Mother asks me to sit with them and talk. I hate it.”’ She said this with a vehemence that Srimathi still remembers. It was obvious that Jayalalithaa felt she was being forced into doing things that went against her nature. Perhaps she also yearned for a normal family life like her other classmates had.
 Jayalalitha
The book follows a neat chronological order of events and does not stray from its course, which, at times makes for a boring read. Perhaps, as someone who has grown up in Chennai, keenly following the events surrounding Jayalalithaa's life (or hearing and reading extensively about it) the book doesn't come as a surprise — instead it's clinical and passive, stopping short when certain events in Jaya's life could've benefitted (the reader) with some much needed poetic elaboration. Perhaps, for people to the north of the Vindhyas, who aren't familiar with politics in the south, this book is a good start. To compare it with Iruvar, the Mani Ratnam film loosely based on the relationship between MGR-Jayalalithaa-Karunanidhi would be injustice, for a movie is treated vastly different from a book and most importantly, Iruvar was really fiction. And we have to remember that this isn't an authorised biogaphy — meaning access to Jayalalithaa, the main source, is missing, as is the access to the key people in her life: her mother and her brother, Sasikala, Shobhan Babu.
 Jayalalitha
Vaasanthi does manage to talk to RM Veerappan, a close personal aide of MGR, who "projected Jayalalithaa as a temptress" and who "was bent on breaking up the relationship at any cost, saying that he needed to protect MGR from an evil called Jayalalithaa", and to the late Solai, who was Jayalalithaa's speech writer when she was the AIADMK’s propaganda secretary. Although the author's sympathy lies with the protagonist — this is best seen when she writes on how RM Veerappan's views on Jayalalithaa influencing MGR seemed "far-fetched", she does dip into her journalistic sensibilities — after the special court indicted her in the hotel case and AIADMK cadre set fire to a bus full of girls of which three were consumed by the flames, she writes that "Jayalalithaa reacted like a bad loser".
 Jayalalitha
Born into a Srirangam-based Tamil Brahmin family in Bangalore, Jayalalithaa ruled the roost in Tamil cinema since her debut with Vennira Aadai (1965) till 1978. She had an image makeover once she met her hero, MGR, which also gave rise to the many ups and downs in her life. When Jayalalithaa first started acting, Vaasanthi describes her as a braveheart, a "remarkably fearless" woman, who if she has made her up mind would continue with it channeling her steely determination. In the chapter 'A Star is Born', she writes:
She belonged to the Mandiam Iyengar community that hailed from Karnataka. But in an article that appeared in a magazine she was quoted as saying, “I am a Tamilian. My mother belongs to Srirangam.” That angered the Kannadigas in Karnataka who believed her to be a Kannadiga. Because of the threats she received she cancelled her scheduled dance programme at the Dasara arts festival in Mysore. Two months later, during the shooting of director Panthulu’s film at the Chamundi studios in Mysore, the organizer of the Dasara arts festival heard she was there, and decided to confront her. Th e studio manager got news that about a hundred protesters were marching towards the studio to beat up Jayalalithaa. So he ordered the gates to be locked. But the hooligans jumped over the gates and entered with lathis in their hands shouting in Kannada: “Where is the bitch?” They barged in, knocking down the guards and journalists standing at the door. Panthulu spoke to them in Kannada and pleaded with them to go away. But they demanded that Jayalalithaa should say sorry for having said that she was not a Kannadiga. Jayalalithaa was neither ruffled nor afraid. She looked straight at them and said in chaste Kannada, “I have not said anything wrong. Why should I apologise? I am a Tamilian and not a Kannadiga!”
 Jayalalitha
From an independent being, Jayalalithaa turned into a puppet in the hands of MGR — he took control over her activities, her finances; in short, he wanted her to be with him till he didn't. Which happened during the time he started the AIADMK on 18 October, 1972, rendering him busy with politics. In the midst of a temporary release from MGR, Vaasanthi writes about how Jayalalithaa got involved with Telugu actor Sobhan Babu, even going as far as arranging a wedding ceremony with him, which, according to some friends quoted in the book, did happen.
The meat of the book focuses on Amma's political career — for those in the dark, she joined the party on 4 June, 1982, gave her maiden speech in Cuddalore ("an impressive, fiery oration"), how she reunited with an estranged MGR, and in the end became his political heir, ousting Janaki Ramachandran, MGR's wife, in the process. As Mukul Kesavan writes in this arresting piece, for The Telegraph,
In republican India, parties founded by individuals — M.G. Ramachandran, N.T. Rama Rao, Kanshi Ram, Mamata Banerjee — never manage to institutionalize succession. The successor is either personally anointed by the leader — Kanshi Ram’s naming of Mayavati in 2001 is a case in point — or the leader’s mantle is claimed through a war of succession. Jayalalithaa is an example of the latter route: she emerged as MGR’s undisputed successor only after fighting and winning a succession battle with his widow. This contest didn’t occur via the internal mechanisms of the party — there were none — but through fission and faction
 Jayalalitha
All her life, Jayalalithaa has been a fighter and this book is proof of that. Whether she was constantly fighting a hate campaign brewing against her in the party or when it seemed that MGR's trust in her was fading or after MGR's untimely death, she has never given up. The one other theme that is a constant in the book is that of loneliness — it goes without saying that people at the top are lonely, and a woman who tries to reach there is even more so. In that way, the story of Jayalalithaa is the story of an everywoman: that of constant struggle, of trying to find approval an acceptance, of trying to make cutthroat decisions without seeming 'monstrous'. It's a book many women will identify with; after all women voters did play a decisive role in voting her back to power in Tamil Nadu.
Vaasanthi writes an objective account of Jayalalithaa's life, no doubt — there's no larger-than-life symbolism of the woman who turned from a glamourous actress to a de-glamourised caretaker of the state (her moniker 'Amma' translates to mother). But how she opted for politics and transformed into a leader, who then became a brand synonymous with populism, needs more sketching in the book.
 Jayalalitha
The book could also do with some airtight editing: at certain incidents Vaasanthi offers us the Tamil words employed by the people (in the book), but mostly she goes with the English translation of it. Instead, if Vaasanthi could've been persuaded to employ the original Tamil words and phrases, coupled with a small glossary at the back, it would've made for some poignant reading. One more aspect that could've been fleshed upon is the dynamic between Karunanidhi and her, one that has constantly defined politics in TN till now. Amma: Jayalalithaa’s Journey from Movie Star to Political Queen could give rise to detailed case studies of the chief minister, her leadership and how the state transformed under her, but till then this book will just have to do.
Amma: Jayalalithaa’s Journey from Movie Star to Political Queen is published by Juggernaut

Tuesday, November 29, 2016

Biography of Jagadish Chandra Bose

Jagadish Chandra Bose
Born: November 30, 1858 

Died: November 23, 1937 

Achievements: He was the first to prove that plants too have feelings. He invented wireless telegraphy a year before Marconi patented his invention. 

Jagdish Chandra Bose was an eminent Indian scientist. He was the first to prove that plants and metals too have feelings. 

Jagdish Chandra Bose was born on November 30, 1858 in Mymensingh (now in Bangladesh). His father Bhagabanchandra Bose was a Deputy Magistrate. Jagadish Chandra Bose had his early education in village school in Bengal medium. In 1869, Jagadish Chandra Bose was sent to Calcutta to learn English and was educated at St.Xavier's School and College. He was a brilliant student. He passed the B.A. in physical sciences in 1879. 

Jagadish Chandra Bose
In 1880, Jagdishchandra Bose went to England. He studied medicine at London University, England, for a year but gave it up because of his own ill health. Within a year he moved to Cambridge to take up a scholarship to study Natural Science at Christ's College Cambridge. In 1885, he returned from abroad with a B.Sc. degree and Natural Science Tripos (a special course of study at Cambridge). 

After his return Jagadish Chandra Bose, was offered lectureship at Presidency College, Calcutta on a salary half that of his English colleagues. He accepted the job but refused to draw his salary in protest. After three years the college ultimately conceded his demand and Jagdish Chandra Bose was paid full salary from the date he joined the college. As a teacher Jagdish Chandra Bose was very popular and engaged the interest of his students by making extensive use of scientific demonstrations. Many of his students at the Presidency College were destined to become famous in their own right. These included Satyendra Nath Bose and Meghnad Saha. In 1894, Jagadish Chandra Bose decided to devote himself to pure research. He converted a small enclosure adjoining a bathroom in the Presidency College into a laboratory. He carried out experiments involving refraction, diffraction and polarization. It would not be wrong to call him as the inventor of wireless telegraphy. In 1895, a year before Guglielmo Marconi patented this invention, he had demonstrated its functioning in public. 

Jagadish Chandra Bose
Jagdish Chandra Bose later switched from physics to the study of metals and then plants. He fabricated a highly sensitive "coherer", the device that detects radio waves. He found that the sensitivity of the coherer decreased when it was used continuously for a long period and it regained its sensitivity when he gave the device some rest. He thus concluded that metals have feelings and memory. 

Jagdish Chandra Bose showed experimentally plants too have life. He invented an instrument to record the pulse of plants and connected it to a plant. The plant, with its roots, was carefully picked up and dipped up to its stem in a vessel containing bromide, a poison. The plant's pulse beat, which the instrument recorded as a steady to-and-fro movement like the pendulum of a clock, began to grow unsteady. Soon, the spot vibrated violently and then came to a sudden stop. The plant had died because of poison. 

Jagadish Chandra Bose
Although Jagdish Chandra Bose did invaluable work in Science, his work was recognized in the country only when the Western world recognized its importance. He founded the Bose Institute at Calcutta, devoted mainly to the study of plants. Today, the Institute carries research on other fields too. 

Jagdish Chandra Bose died on November 23, 1937.