The viscosities of some fluids

Fluid                    T(oC)     Viscosity (mPl)

Water              20       1.0 
                   100       0.3 

Blood              37       2.7 

Machine Oil      16       113 
                    38       34 

Glycerine               20        830

Honey                                    200

Air                       0              0.017
                             40            0.019

Daniel Bernoulli (1700-1782)

Daniel Bernoulli was a Swiss scientist and mathematician who along with Leonard Euler had the distinction of winning the French Academy prize for mathematics ten times. He also studied medicine and served as a professor of anatomy and botany for a while at Basle, Switzerland. His most well known work was in hydrodynamics, a subject he developed from a single principle: the conservation of energy. His work included calculus, probability, the theory of vibrating strings, and applied mathematics. He has been called the founder of mathematical physics.

Archimedes (287 – 212 B.C.)

Archimedes was a Greek philosopher, mathematician, scientist and engineer. He invented the catapult and devised a system of pulleys and levers to handle heavy loads. The king of his native city Syracuse, Hiero II asked him to determine if his gold crown was alloyed with some cheaper metal such as silver without damaging the crown. The partial loss of weight he experienced while lying in his bathtub suggested a solution to him. According to legend, he ran naked through the streets of Syracuse exclaiming “Eureka, eureka!”, which means “I have found it, I have found it!”

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Robert Hooke (1635 – 1703 A.D.)

Robert Hooke was born on July 18, 1635 in Freshwater, Isle of Wight. He was one of the most brilliant and versatile seventeenth century English scientists. He attended Oxford University but never graduated. Yet he was an extremely talented inventor, instrument-maker and building designer. He assisted Robert Boyle in the construction of Boylean air pump. In 1662, he was appointed as Curator of Experiments to the newly founded Royal Society. In 1665, he became Professor of Geometry in Gresham College where he carried out his astronomical observations. He built a Gregorian reflecting telescope; discovered the fifth star in the trapezium and an asterism in the constellation Orion; suggested that Jupiter rotates on its axis; plotted detailed sketches of Mars which were later used in the 19th century to determine the planet’s rate of rotation; stated the inverse square law to describe planetary motion, which Newton modified later etc. He was elected Fellow of Royal Society and also served as the Society’s Secretary from 1667 to 1682. In his series of observations presented in Micrographia, he suggested wave theory of light and first used the word ‘cell’ in a biological context as a result of his studies of cork.
Robert Hooke is best known to physicists for his discovery of law of elasticity: Ut tensio, sic vis (This is a Latin expression and it means as the distortion, so the force). This law laid the basis for studies of stress and strain and for understanding the elastic materials.

Johannes Kepler (1571–1630)

He was a scientist of German origin. He formulated the three laws of planetary motion based on the painstaking observations of Tycho Brahe and coworkers. Kepler himself was an assistant to Brahe and it took him sixteen long years to arrive at the three planetary laws. He is also known as the founder of geometrical optics, being the first to describe what happens to light after it enters a telescope.

India’s Leap into Space

India entered the space age with the launching of the low orbit satellite Aryabhatta in 1975. In the first few years of its programme the launch vehicles were provided by the erstwhile Soviet Union. Indigenous launch vehicles were employed in the early 1980’s to send the Rohini series of satellites into space. The programme to send polar satellites into space began in late 1980’s. A series of satellites labelled IRS (Indian Remote Sensing Satellites) have been launched and this programme is expected to continue in future. The satellites have been employed for surveying, weather prediction and for carrying out experiments in space. The INSAT (Indian National Satellite) series of satellites were designed and made operational for communications and weather prediction purposes beginning in 1982. European launch vehicles have been employed in the INSAT series. India tested its geostationary launch capability in 2001 when it sent an experimental communications satellite (GSAT-1) into space. In 1984 Rakesh Sharma became the first Indian astronaut. The Indian Space Research Organisation (ISRO) is the umbrella organisation that runs a number of centre. Its main lauch centre at Sriharikota (SHAR) is 100 km north of Chennai. The National Remote Sensing Agency (NRSA) is near Hyderabad. Its national centre for research in space and allied sciences is the Physical Research Laboratory (PRL) at Ahmedabad.

Isaac Newton (1642 – 1727)

Isaac Newton was born in Woolsthorpe, England in 1642, the year Galileo died. His extraordinary mathematical ability and mechanical aptitude remained hidden from others in his school life. In 1662, he went to Cambridge for undergraduate studies. A plague epidemic in 1665 forced the university town to close and Newton had to return to his mother’s farm. There in two years of solitude, his dormant creativity blossomed in a deluge of fundamental discoveries in mathematics and physics : binomial theorem for negative and fractional exponents, the beginning of calculus, the inverse square law of gravitation, the spectrum of white light, and so on. Returning to Cambridge, he pursued his investigations in optics and devised a reflecting telescope.
In 1684, encouraged by his friend Edmund Halley, Newton embarked on writing what was to be one of the greatest scientific works ever published : The Principia Mathematica. In it, he enunciated the three laws of motion and the universal law of gravitation, which explained all the three Kepler’s laws of planetary motion. The book was packed with a host of path-breaking achievements : basic principles of fluid mechanics, mathematics of wave motion, calculation of masses of the earth, the sun and other planets, explanation of the precession of equinoxes, theory of tides, etc. In 1704, Newton brought out another masterpiece Opticks that summarized his work on light and colour.
The scientific revolution triggered by Copernicus and steered vigorously ahead by Kepler and Galileo
was brought to a grand completion by Newton. Newtonian mechanics unified terrestrial and celestial
phenomena. The same mathematical equation governed the fall of an apple to the ground and the motion of the moon around the earth. The age of reason had dawned.

Galileo Galilei (1564 - 1642)

Galileo Galilei, born in Pisa, Italy in 1564 was a key figure in the scientific revolution in Europe about four centuries ago. Galileo proposed the concept of acceleration. From experiments on motion of bodies on inclined planes or falling freely, he contradicted the Aristotelian notion that a force was required to keep a body in motion, and that heavier bodies fall faster than lighter bodies under gravity. He thus arrived at the law of inertia that was the starting point of the subsequent epochal work of Isaac Newton.
Galileo’s discoveries in astronomy were equally revolutionary. In 1609, he designed his own telescope (invented earlier in Holland) and used it to make a number of startling observations : mountains and depressions on the surface of the moon; dark spots on the sun; the moons of Jupiter and the phases of Venus. He concluded that the Milky Way derived its luminosity because of a large number of stars not visible to the naked eye.
In his masterpiece of scientific reasoning : Dialogue on the Two Chief World Systems, Galileo advocated the heliocentric theory of the solar system proposed by Copernicus, which eventually got universal acceptance. With Galileo came a turning point in the very method of scientific inquiry. Science was no longer merely observations of nature and inferences from them. Science meant devising and doing experiments to verify or refute theories. Science meant measurement of quantities and a search for mathematical relations between them. Not undeservedly, many regard Galileo as the father of modern science.

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Sir C.V. Raman (1888-1970)

Chandrashekhara Venkata Raman was born on 07 Nov 1888 in Thiruvanaikkaval. He finished his schooling by the age of eleven. He graduated from Presidency College, Madras. After finishing his education he joined financial services of the Indian Government.
While in Kolkata, he started working on his area of interest at Indian Association for Cultivation of Science founded by Dr. Mahendra Lal Sirkar, during his evening hours. His area of interest included vibrations, variety of musical instruments, ultrasonics, diffraction and so on.
In 1917 he was offered Professorship at Calcutta University. In 1924 he was elected ‘Fellow’ of the Royal Society of London and received Nobel prize in Physics in 1930 for his discovery, now known as Raman Effect.
The Raman Effect deals with scattering of light by molecules of a medium when they are excited to vibrational energy levels. This work opened totally new avenues for research for years to come. He spent his later years at Bangalore, first at Indian Institute of Science and then at Raman Research Institute. His work has inspired generation of young students.

FORCES

Gravitational Force
The gravitational force is the force of mutual attraction between any two objects by virtue of their masses. It is a universal force. Every object experiences this force due to every other object in the universe.


Electromagnetic Force
Electromagnetic force is the force between charged particles. In the simpler case when charges are at rest, the force is given by Coulomb’s law : attractive for unlike charges and repulsive for like charges. Charges in motion produce magnetic effects and a magnetic field gives rise to a force on a moving charge.


Strong Nuclear Force
The strong nuclear force binds protons and neutrons in a nucleus. It is evident that without some attractive force, a nucleus will be unstable due to the electric repulsion between its protons. This attractive force cannot be gravitational since force of gravity is negligible compared to the electric force.


Weak Nuclear Force
The weak nuclear force appears only in certain nuclear processes such as the β-decay of a nucleus. In β-decay, the nucleus emits an electron and an uncharged particle called neutrino. The weak nuclear force is not as weak as the gravitational force, but much weaker than the strong nuclear and electromagnetic forces.

Satyendranath Bose (1894-1974)

  Satyendranath Bose, born in Calcutta in 1894, is among the great Indian physicists who made a fundamental contribution to the advance of science in the twentieth century. An outstanding student throughout, Bose started his career in 1916 as a lecturer in physics in Calcutta University; five years later he joined Dacca University. Here in 1924, in a brilliant flash of insight, Bose gave a new derivation of Planck’s law, treating radiation as a gas of photons and employing new statistical methods of counting of photon states. He wrote a short paper on the subject and sent it to Einstein who immediately recognised its great significance, translated it in German and forwarded it for publication. Einstein then applied the same method to a gas of molecules. The key new conceptual ingredient in Bose’s work was that the particles were regarded as indistinguishable, a radical departure from the assumption that underlies the classical Maxwell Boltzmann statistics. It was soon realised that the new Bose-Einstein statistics was applicable to particles with integers spins, and a new quantum statistics (Fermi-Dirac statistics) was needed for particles with half integers spins satisfying Pauli’s exclusion principle. Particles with integers spins are now known as bosons in honour of Bose.
An important consequence of Bose-Einstein statistics is that a gas of molecules below a certain temperature will undergo a phase transition to a state where a large fraction of atoms populate the same lowest energy state. Some seventy years were to pass before the pioneering ideas of Bose, developed further by Einstein, were dramatically confirmed in the observation of a new state of matter in a dilute gas of ultra cold alkali atoms - the Bose-Eintein condensate.

Technology - Scientific principle(s)

Steam engine -Laws of thermodynamics

Nuclear reactor- Controlled nuclear fission

Radio and Television - Generation, propagation and detection of electromagnetic waves

Computers - Digital logic

Lasers Light amplification by stimulated emission of radiation

Production of ultra high magnetic fields - Superconductivity

Rocket propulsion - Newton’s laws of motion

Electric generator- Faraday’s laws of electromagnetic induction

Hydroelectric power- Conversion of gravitational potential energy into electrical energy

Aeroplane - Bernoulli’s principle in fluid dynamics

Particle accelerators - Motion of charged particles in electromagnetic fields

Sonar - Reflection of ultrasonic waves

Optical fibres - Total internal reflection of light

Non-reflecting coatings - Thin film optical interference

Electron microscope - Wave nature of electrons

Photocell- Photoelectric effect

Fusion test reactor (Tokamak)- Magnetic confinement of plasma

Giant Metrewave Radio Telescope (GMRT) - Detection of cosmic radio waves

Bose-Einstein condensate -Trapping and cooling of atoms by laser beams and magnetic fields.

Major contribution/discovery

Archimedes - Principle of buoyancy; Principle of the lever- Greece 

Galileo Galilei - Law of inertia - Italy 

Christiaan Huygens - Wave theory of light - Holland 

Isaac Newton  - Universal law of gravitation; Laws of motion; Reflecting telescope - U.K. 

Michael Faraday -Laws of electromagnetic induction - U.K. 

James Clerk Maxwell - Electromagnetic theory; Light-an electromagnetic wave - U.K. 

Heinrich Rudolf Hertz -  Generation of electromagnetic waves - Germany 

J.C. Bose - Ultra short radio waves - India 

W.K. Roentgen - X-rays - Germany 

J.J. Thomson - Electron - U.K. 

Marie Sklodowska Curie -Discovery of radium and polonium; Studies on natural radioactivity -Poland 

Albert Einstein  Explanation of photoelectric effect; - Theory of relativity - Germany


Victor Francis Hess- Cosmic radiation- Austria

R.A. Millikan -Measurement of electronic charge- U.S.A.

Ernest Rutherford - Nuclear model of atom- New Zealand

Niels Bohr- Quantum model of hydrogen atom- Denmark

C.V. Raman- Inelastic scattering of light by molecules -India

Louis Victor de Borglie -  Wave nature of matter -  France

M.N. Saha - Thermal ionisation-  India

S.N. Bose- Quantum statistics- India

Wolfgang Pauli- Exclusion principle - Austria

Enrico Fermi- Controlled nuclear fission-Italy

Werner Heisenberg - Quantum mechanics; Uncertainty principle - Germany

Paul Dirac -Relativistic theory of electron; Quantum statistics - U.K.

Edwin Hubble - Expanding universe  U.S.A.

Ernest Orlando Lawrence-  Cyclotron-  U.S.A.

James Chadwick - Neutron- U.K.

Hideki Yukawa -Theory of nuclear forces -Japan

Homi Jehangir Bhabha - Cascade process of cosmic radiation- India

Lev Davidovich Landau -Theory of condensed matter; Liquid helium- Russia

S. Chandrasekhar- Chandrasekhar limit, structure and evolution of stars - India

John Bardeen -Transistors; Theory of super conductivity- U.S.A.

C.H. Townes - Maser; Laser- U.S.A.

Abdus Salam- Unification of weak and electromagnetic interactions - Pakistan

INDIA’S ATOMIC ENERGY PROGRAMME

The atomic energy programme in India was launched around the time of independence under the leadership of Homi J. Bhabha (1909-1966). An early historic achievement was the design and construction of the first nuclear reactor in India (named Apsara) which went critical on August 4, 1956. It used enriched uranium as fuel and water as moderator. Following this was another notable landmark: the construction of CIRUS (Canada India Research U.S.) reactor in 1960. This 40 MW reactor used natural uranium as fuel and heavy water as moderator. Apsara and CIRUS spurred research in a wide range of areas of basic and applied nuclear science. An important milestone in the first two decades of the programme was the indigenous design and construction of the plutonium plant at Trombay, which ushered in the technology of fuel reprocessing (separating useful fissile and fertile nuclear materials from the spent fuel of a reactor) in India. Research reactors that have been subsequently commissioned include ZERLINA, PURNIMA (I, II and III), DHRUVA and KAMINI. KAMINI is the country’s first large research reactor that uses U-233 as fuel. As the name suggests, the primary objective of a research reactor is not generation of power but to provide a facility for research on different aspects of nuclear science and technology. Research reactors are also an excellent source for production of a variety of radioactive isotopes that find application in diverse fields: industry, medicine and agriculture.

The main objectives of the Indian Atomic Energy programme are to provide safe and reliable electric power for the country’s social and economic progress and to be selfreliant in all aspects of nuclear technology. Exploration of atomic minerals in India undertaken since the early fifties has indicated that India has limited reserves of uranium, but fairly abundant reserves of thorium. Accordingly, our country has adopted a threestage strategy of nuclear power generation. The first stage involves the use of natural uranium as a fuel, with heavy water as moderator. The Plutonium-239 obtained from reprocessing of the discharged fuel from the reactors then serves as a fuel for the second stage — the fast breeder reactors. They are so called because they use fast neutrons for sustaining the chain reaction (hence no moderator is needed) and, besides generating power, also breed more fissile species (plutonium) than they consume. The third stage, most significant in the long term, involves using fast breeder reactors to produce fissile Uranium-233 from Thorium-232 and to build power reactors based on them.

India is currently well into the second stage of the programme and considerable work has also been done on the third — the thorium utilisation — stage. The country has mastered the complex technologies of mineral exploration and mining, fuel fabrication, heavy water production, reactor design, construction and operation, fuel reprocessing, etc. Pressurised Heavy Water Reactors (PHWRs) built at different sites in the country mark the accomplishment of the first stage of the programme. India is now more than self-sufficient in heavy water production. Elaborate safety measures both in the design and operation of reactors, as also adhering to stringent standards of radiological protection are the hallmark of the Indian Atomic Energy Programme.

FASTER AND SMALLER: THE FUTURE OF COMPUTER TECHNOLOGY

The Integrated Chip (IC) is at the heart of all computer systems. In fact ICs are found in almost all electrical devices like cars, televisions, CD players, cell phones etc. The miniaturisation that made the modern personal computer possible could never have happened without the IC. ICs are electronic devices that contain many transistors, resistors, capacitors, connecting wires – all in one package. You must have heard of the microprocessor. The microprocessor is an IC that processes all information in a computer, like keeping track of what keys are pressed, running programmes, games etc. The IC was first invented by Jack Kilky at Texas Instruments in 1958 and he was awarded Nobel Prize for this in 2000. ICs are produced on a piece of semiconductor crystal (or chip) by a process called photolithography. Thus, the entire Information Technology (IT) industry hinges on semiconductors. Over the years, the complexity of ICs has increased while the size of its features continued to shrink. In the past five decades, a dramatic miniaturisation in computer technology has made modern day computers faster and smaller.
In the 1970s, Gordon Moore, co-founder of INTEL, pointed out that the memory capacity of a chip (IC) approximately doubled every one and a half years. This is popularly known as Moore’s law. The number of transistors per chip has risen exponentially and each year computers are becoming more powerful, yet cheaper than the year before. It is intimated from current trends that the computers available in 2020 will operate at 40 GHz (40,000 MHz) and would be much smaller, more efficient and less expensive than present day computers. The explosive growth in the semiconductor industry and computer technology is best expressed by a famous quote from Gordon Moore: “If the auto industry advanced as rapidly as the semiconductor industry, a Rolls Royce would get half a million miles per gallon, and it would be cheaper to throw it away than to park it”.

Nuclei

1. The density of nuclear matter is independent of the size of the nucleus. The mass density of the atom does not follow this rule.

2. The radius of a nucleus determined by electron scattering is found to be slightly different from that determined by alpha-particle scattering.This is because electron scattering senses the charge distribution of the nucleus, whereas alpha and similar particles sense the nuclear matter.

3. After Einstein showed the equivalence of mass and energy, E = mc2, we cannot any longer speak of separate laws of conservation of mass and conservation of energy, but we have to speak of a unified law of conservation of mass and energy. The most convincing evidence that this principle operates in nature comes from nuclear physics. It is central to our understanding of nuclear energy and harnessing it as a source of power. Using the principle, Q of a nuclear process (decay or reaction) can be expressed also in terms of initial and final masses.

4. The nature of the binding energy (per nucleon) curve shows that exothermic nuclear reactions are possible, when two light nuclei fuse or when a heavy nucleus undergoes fission into nuclei with intermediate mass.

5. For fusion, the light nuclei must have sufficient initial energy to overcome the coulomb potential barrier. That is why fusion requires very high temperatures.

6. Although the binding energy (per nucleon) curve is smooth and slowly varying, it shows peaks at nuclides like 4He, 16O etc. This is considered as evidence of atom-like shell structure in nuclei.

7. Electrons and positron are a particle-antiparticle pair. They are identical in mass; their charges are equal in magnitude and opposite. ( It is found that when an electron and a positron come together, they annihilate each other giving energy in the form of gamma-ray photons.)

8. In â--decay (electron emission), the particle emitted along with electron is anti-neutrino (ν ). On the other hand, the particle emitted in β+- decay (positron emission) is neutrino (ν). Neutrino and anti-neutrino are a particle-antiparticle pair. There are anti particles associated with every particle. What should be antiproton which is the anti particle of the proton?

9. A free neutron is unstable (n→p+e– +ν ). But a similar free proton decay is not possible, since a proton is (slightly) lighter than a neutron.

10. Gamma emission usually follows alpha or beta emission. A nucleus in an excited (higher) state goes to a lower state by emitting a gamma photon. A nucleus may be left in an excited state after alpha or beta emission. Successive emission of gamma rays from the same nucleus is a clear proof that nuclei also have discrete energy levels as do the atoms.

11. Radioactivity is an indication of the instability of nuclei. Stability requires the ratio of neutron to proton to be around 1:1 for light nuclei. This ratio increases to about 3:2 for heavy nuclei. (More neutrons are required to overcome the effect of repulsion among the protons.) Nuclei which are away from the stability ratio, i.e., nuclei which have an excess of neutrons or protons are unstable. In fact,
only about 10% of knon isotopes (of all elements), are stable. Others have been either artificially produced in the laboratory by bombarding α, p, d, n or other particles on targets of stable nuclear species or identified in astronomical observations of matter in the universe.

Marie Sklodowska Curie (1867-1934)

 Born in Poland. She is recognised both as a physicist and as a chemist. The discovery of radioactivity by Henri Becquerel in 1896 inspired Marie and her husband Pierre Curie in their researches and analyses which led to the isolation of radium and polonium elements. She was the first person to be awarded two Nobel Prizes- for Physics in 1903 and for Chemistry in 1911.

Atom

1. Atom, as a whole, is electrically neutral and therefore contains equal amount of positive and negative charges.

2. In Thomson’s model, an atom is a spherical cloud of positive charges with electrons embedded in it.

3. In Rutherford’s model, most of the mass of the atom and all its positive charge are concentrated in a tiny nucleus (typically one by ten thousand the size of an atom), and the electrons revolve around it.

4. Rutherford nuclear model has two main difficulties in explaining the structure of atom: (a) It predicts that atoms are unstable because the accelerated electrons revolving around the nucleus must spiral into the nucleus. This contradicts the stability of matter. (b) It cannot explain the characteristic line spectra of atoms of different elements.

5. Atoms of each element are stable and emit characteristic spectrum. The spectrum consists of a set of isolated parallel lines termed as line spectrum. It provides useful information about the atomic structure.

LASER LIGHT

The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. Since its development in 1960, it has entered into all areas of science and technology. It has found applications in physics, chemistry, biology, medicine, surgery, engineering, etc. There are low power lasers, with a power of 0.5 mW, called pencil lasers, which serve as pointers. There are also lasers of different power, suitable for delicate surgery of eye or glands in the stomach. Finally, there are lasers which can cut or weld steel.
Light is emitted from a source in the form of packets of waves. Light coming out from an ordinary source contains a mixture of many wavelengths. There is also no phase relation between the various waves. Therefore, such light, even if it is passed through an aperture, spreads very fast and the beam size increases rapidly with distance. In the case of laser light, the wavelength of each packet is almost the same. Also the average length of the packet of waves is much larger. This means that there is better phase correlation over a longer duration of time. This results in reducing the divergence of a laser beam substantially.
If there are N atoms in a source, each emitting light with intensity I, then the total intensity produced by an ordinary source is proportional to NI, whereas in a laser source, it is proportional to N2I. Considering that N is very large, we see that the light from a laser can be much stronger than that from an ordinary source.
When astronauts of the Apollo missions visited the moon, they placed a mirror on its surface, facing the earth. Then scientists on the earth sent a strong laser beam, which was reflected by the mirror on the moon and received back on the earth. The size of the reflected laser beam and the time taken for the round trip were measured. This allowed a very accurate determination of (a) the extremely small divergence of a laser beam and (b) the distance of the moon from the earth.

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Niels Henrik David Bohr (1885 – 1962)

 Danish physicist who explained the spectrum of hydrogen atom based on quantum ideas. He gave a theory of nuclear fission based on the liquiddrop model of nucleus. Bohr contributed to the clarification of conceptual problems in quantum mechanics, in particular by proposing the complementary principle.

Ernst Rutherford (1871 – 1937)

 British physicist who did pioneering work on radioactive radiation. He discovered alpha-rays and beta-rays. Along with Federick Soddy, he created the modern theory of radioactivity. He studied the ‘emanation’ of thorium and discovered a new noble gas, an isotope of radon, now known as thoron. By scattering alpha-rays from the metal foils, he discovered the atomic nucleus and proposed the plenatery model of the atom. He also estimated the approximate size of the nucleus.

Thomas Young (1773 – 1829)

 English physicist, physician and Egyptologist. Young worked on a wide variety of scientific problems, ranging from the structure of the eye and the mechanism of vision to the decipherment of the Rosetta stone. He revived the wave theory of light and recognised that interference phenomena provide proof of the wave properties of light.

Christiaan Huygens (1629 – 1695)

 Dutch physicist, astronomer, mathematician and the founder of the wave theory of light. His book, Treatise on light, makes fascinating reading even today. He brilliantly explained the double refraction shown by the mineral calcite in this work in addition to reflection and refraction. He was the first to analyse circular and simple harmonic motion and designed and built improved clocks and telescopes. He discovered the true geometry of Saturn’s rings.

The Internet

It is a system with billions of users worldwide. It permits communication and sharing of all types of information between any two or more computers connected through a large and complex network. It was started in 1960’s and opened for public use in 1990’s. With the passage of time it has witnessed tremendous growth and it is still expanding its reach. Its applications include

(i) E mail – It permits exchange of text/graphic material using email software. We can write a letter and send it to the recipient through ISP’s (Internet Service Providers) who work like the dispatching and receiving post offices.

(ii) File transfer – A FTP (File Transfer Programmes) allows transfer of files/software from one computer to another connected to the Internet.

(iii) World Wide Web (WWW) – Computers that store specific information for sharing with others provide websites either directly or through web service providers. Government departments, companies, NGO’s (Non-Government Organisations) and individuals can post information about their activities for restricted or free use on their websites. This information becomes accessible to the users. Several search engines like Google, Yahoo! etc. help us in finding information by listing the related websites. Hypertext is a powerful feature of the web that automatically links relevant information from one page on the web to another using HTML (hypertext markup language).

(iv) E-commerce – Use of the Internet to promote business using electronic means such as using credit cards is called E-commerce. Customers view images and receive all the information about various products or services of companies through their websites. They can do on-line shopping from home/office. Goods are dispatched or services are provided by the company through mail/courier.

(v) Chat – Real time conversation among people with common interests through typed
messages is called chat. Everyone belonging to the chat group gets the message
instantaneously and can respond rapidly.

Facsimile (FAX)
It scans the contents of a document (as an image, not text) to create electronic signals. These signals are then sent to the destination (another FAX machine) in an orderly manner using telephone lines. At the destination, the signals are reconverted into a replica of the original document. Note that FAX provides image of a static document unlike the image provided by television of objects that might be dynamic.

Mobile telephony
The concept of mobile telephony was developed first in 1970’s and it was fully implemented in the following decade. The central concept of this system is to divide the service area into a suitable number of cells centred on an office called MTSO (Mobile Telephone Switching Office). Each cell contains a low-power transmitter called a base station and caters to a large number of mobile receivers (popularly called cell phones). Each cell could have a service area of a few square kilometers or even less depending upon the number of customers. When a mobile receiver crosses the coverage area of one base station, it is necessary for the mobile user to be transferred to another base station. This procedure is called handover or handoff. This process is carried out very rapidly, to the extent that the consumer does not even notice it. Mobile telephones operate typically in the UHF range of frequencies (about 800-950 MHz).

Jagadis Chandra Bose (1858 – 1937)

He developed an apparatus for generating ultra short electro-magnetic waves and studied their quasioptical properties. He was said to be the first to employ a semiconductor like galena as a self recovering detector of electromagnetic waves. Bose published three papers in the British magazine, ‘The Electrician’ of 27 Dec. 1895. His invention was published in the ‘Proceedings of The Royal Society’ on 27 April 1899 over two years before Marconi’s first wireless communication on 13 December 1901. Bose also invented highly sensitive instruments for the detection of minute responses by living organisms to external stimulii and established parallelism between animal and plant tissues.

BASIC TERMINOLOGY USED IN ELECTRONIC COMMUNICATION SYSTEMS

(i) Transducer: Any device that converts one form of energy into another can be termed as a transducer. In electronic communication systems, we usually come across devices that have either their inputs or outputs in the electrical form. An electrical transducer may be defined as a device that converts some physical variable (pressure, displacement, force, temperature, etc) into corresponding variations in the electrical signal at its output.

(ii) Signal: Information converted in electrical form and suitable for transmission is called a signal. Signals can be either analog or digital. Analog signals are continuous variations of voltage or current. They are essentially single-valued functions of time. Sine wave is a fundamental analog signal. All other analog signals can be fully understood in terms of their sine wave components. Sound and picture signals in TV are analog in nature. Digital signals are those which can take only discrete stepwise values. Binary system that is extensively used in digital electronics employs just two levels of a signal. ‘0’ corresponds to a low level and ‘1’ corresponds to a high level of voltage/ current. There are several coding schemes useful for digital communication. They employ suitable combinations of number systems such as the binary coded decimal (BCD). American Standard Code for Information Interchange (ASCII) is a universally popular digital code to represent numbers, letters and certain characters.

(iii) Noise: Noise refers to the unwanted signals that tend to disturb the transmission and processing of message signals in a communication system. The source generating the noise may be located inside or outside the system.

(iv) Transmitter: A transmitter processes the incoming message signal so as to make it suitable for transmission through a channel and subsequent reception.

(v) Receiver: A receiver extracts the desired message signals from the received signals at the channel output.

(vi) Attenuation: The loss of strength of a signal while propagating through a medium is known as attenuation.


(vii) Amplification: It is the process of increasing the amplitude (andconsequently the strength) of a signal using an electronic circuit called the amplifier. Amplification is necessary to compensate for the attenuation of the signal in communication systems. The energy needed for additional signal strength is obtained from a DC power source. Amplification is done at a place between the source and the destination wherever signal strength becomes weaker than the required strength.

(viii) Range: It is the largest distance between a source and a destination up to which the signal is received with sufficient strength.

(ix) Bandwidth: Bandwidth refers to the frequency range over which an equipment operates or the portion of the spectrum occupied by the signal.

(x) Modulation: The original low frequency message/information signal cannot be transmitted to long distances. Therefore, at the transmitter, information contained in the low frequency message signal is superimposed on a high frequency wave, which acts as a carrier of the information. This process is known as modulation. As will be explained later, there are several types of modulation, abbreviated as AM, FM and PM.

(xi) Demodulation: The process of retrieval of information from the carrier wave at the receiver is termed demodulation. This is the reverse process of modulation.

(xii) Repeater: A repeater is a combination of a receiver and a transmitter. A repeater, picks up the signal from the transmitter, amplifies and retransmits it to the receiver sometimes with a change in carrier frequency. Repeaters are used to extend the range of a communication system as shown in Fig. 15.2. A communication satellite is essentially a repeater station in space.

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SOME MAJOR MILESTONES IN THE HISTORY OF COMMUNICATION

Around 1565 A.D.-The reporting of the delivery of a child by queen using drum beats from a distant place to King Akbar.-It is believed that minister Birbal experimented with the arrangement to decide the number of drummers posted between the place where the queen stayed and the place where the king stayed.

1835 - Invention of telegraph by Samuel F.B. Morse and Sir Charles Wheatstone - It resulted in tremendous growth of messages through post offices and reduced physical travel of messengers considerably.

1876 - Telephone invented by Alexander Graham Bell and Antonio Meucci - Perhaps the most widely used means of communication in the history of mankind.

1895 - Jagadis Chandra Bose and Guglielmo Marconi demonstrated wireless telegraphy. - It meant a giant leap – from an era of communication using wires to communicating without using wires (wireless)

1936 - Television broadcast(John Logi Baird) - First television broadcast by BBC

1955 - First radio FAX transmitted across continent.(Alexander Bain) - The idea of FAX transmission was patented by Alexander Bain in 1843.

1968 - ARPANET- the first internet came into existence(J.C.R. Licklider) - ARPANET was a project undertaken by the U.S. defence department. It allowed file transfer from one computer to another connected to the network.

1975 - Fiber optics developed at Bell Laboratories - Fiber optical systems are superior and
more economical compared to traditional communication systems.

1989-91 - Tim Berners-Lee invented the World Wide Web - WWW may be regarded as the mammoth
encyclopedia of knowledge accessible to everyone round the clock throughout the year.

Louis Victor de Broglie (1892 – 1987)

 French physicist who put forth revolutionary idea of wave nature of matter. This idea was developed by Erwin Schródinger into a fullfledged theory of quantum mechanics commonly known as wave mechanics. In 1929, he was awarded the Nobel Prize in Physics for his discovery of the wave nature of electrons.

Albert Einstein (1879 – 1955)

 Albert Einstein, born in Ulm, Germany in 1879, is universally regarded as one of the greatest physicists of all time. His astonishing scientific career began with the publication of three path-breaking papers in 1905. In the first paper, he introduced the notion of light quanta (now called photons) and used it to explain the features of photoelectric effect that the classical wave theory of radiation could not account for. In the second paper, he developed a theory of Brownian motion that was confirmed experimentally a few years later and provided a convincing evidence of the atomic picture of matter. The third paper gave birth to the special theory of relativity that made Einstein a legend in his own life time. In the next decade, he explored the consequences of his new theory which included, among other things, the mass-energy equivalence enshrined in his famous equation E = mc2. He also created the general version of relativity (The General Theory of Relativity), which is the modern theory of gravitation. Some of Einstein’s most significant later contributions are: the notion of stimulated emission introduced in an alternative derivation of Planck’s blackbody radiation law, static model of the universe which started modern cosmology, quantum statistics of a gas of massive bosons, and a critical analysis of the foundations of quantum mechanics. The year 2005 was declared as International Year of Physics, in recognition of Einstein’s monumental contribution to physics, in year 1905, describing revolutionary scientific ideas that have since influenced all of modern physics.

Charles Augustin de Coulomb (1736 – 1806)

Coulomb, a French physicist, began his career as a military engineer in the West Indies. In 1776, he returned to Paris and retired to a small estate to do his scientific research. He invented a torsion balance to measure the quantity of a force and used it for determination of forces of electric attraction or repulsion between small charged spheres. He thus arrived in 1785 at the inverse square law relation, now known as Coulomb’s law. The law had been anticipated by Priestley and also by Cavendish earlier, though Cavendish never published his results. Coulomb also found the inverse square law of force between unlike and like magnetic poles.

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ABOUT SHARE

Company: An organisation consisting of individuals called ‘shareholders’ by virtue of their holding the shares of a company, who can act as one legal person as regards its business through an elected board of directors.

Share: Fractional part of the capital, and forms the basis of ownership in a company; shares are generally of two types, viz. equity shares and preference shares, according to the provisions of The Companies Act, 1956. Preference shares again are of different types based on varying shades of rights attached to them.
Share Capital of a company is collected by issuing shares to either a select group of persons through the route of private placements and/or offered to the public for subscription. Thus, the issue of shares is basic to the capital of a company. Shares are issued either for cash or for consideration other than cash, the former being more common. Shares are said to be issued for consideration other than cash when a company purchases business, or some asset/assets, and the vendors have agreed to receive payment in the form of fully paid shares of a company.

Stages of Share Issue: The issue of shares for cash is required to be made in strict conformity with the procedure laid down by law for the same. When shares are issued for cash, the amount on them can be collected at one or more of the following stages:
(i) Application for shares
(ii) Allotment of shares
(iii) Call/Calls on shares.

Calls in arrears: Sometimes, the full amount called on allotment and/or call (calls) is not received from the allottees/shareholders. The amount not so received are cumulatively called ‘Unpaid calls’ or ‘Calls-in-Arrears’. However, it is not mandatory for a company to maintain a separate Calls-in-Arrears Account. There are also instances where some shareholders consider it descreet to pay a part or whole of the amount not yet called-up on the shares allotted to them. Any amount paid by a shareholder in the excess of the amount due from him on allotment/call (calls) is known as ‘Calls-in-Advance’ for which a separate account is maintained. A company has the power to charge interest on calls-in-arrears and is under an obligation to pay interest on calls-in-advance if it accepts them in accordance with the provisions of Articles of Association.

Oversubscription: It is possible for the shares of some companies to be oversubscribed which means that applications for more shares are received than the number offered for subscription through the prospectus. Under such a condition, the alternatives available to the directors are as follows :
(i) They can accept some applications in full and totally reject the others,
(ii) A pro-rata distribution can be made by them,
(iii) A combination of the above two alternatives can be adopted by them.
If the amount of minimum subscription is not received to the extent of 90%, the issue devolves. In case the applications received are less than the number of shares offered to the public, the issue is termed as ‘under subscribed’.

Issue of Shares at Premium: Irrespective of the fact that shares have been issued for consideration other than cash, they can be issued either at par or at premium. The issue of shares at par implies that the shares have been issued for an amount exactly equal to their face or nominal value. In case shares are issued at a premium, i.e. at an amount more than the nominal or par value of shares, the amount of
premium is credited to a separate account called ‘Securities Premium Account’, the use of which is strictly regulated by law.

Issue of Shares at Discount: Shares can as well be issued at a discount, i.e. on an amount less than the nominal or par value of shares provided the company fully complies with the provisions laid down by law with regard to the same. Apart from such compliance, shares of a company cannot ordinarily be issued at a discount. When shares are issued at a discount, the amount of discount is debited to ‘Discount on Issue of Share Account’, which is in the nature of capital loss for the company.

Forfeiture of Shares: Sometimes, shareholders fail to pay one or more instalments on shares allotted to them. In such a case, the company has the authority to forfeit shares of the defaulters. This is called ‘Forfeiture of Shares’. Forfeiture means the cancellation of allotment due to breach of contract and to treat the amount already received on such shares as forfeited to the company. The precise accounting treatment of share forfeiture depends upon the conditions on which the shares have been issued — at par, premium or discount. Generally speaking, accounting treatment on forfeiture is to reverse the entries passed till the stage of forfeiture, the amount already received on the shares being credited to Forfeited Shares Account.

Re-issue of Shares: The management of a company is vested with the power to reissue the shares once forfeited by it, subject of course, to the terms and conditions in the articles of association relating to the same. The shares can be reissued even at a discount provided the amount of discount allowed does not exceed the credit balance of forfeited shares’ account relating to shares being reissued. Therefore, discount allowed on the reissue of forfeited shares is debited to forfeited shares’ account. Once all the forfeited shares have been reissued, any credit balance on forfeited shares’ account is transferred to Capital Reserve representing profit on forfeiture of shares. In the event of all forfeited share not being reissued, the credit amount on forfeited shares’ account relating to shares yet to be reissued is carried forward and the remaining balance on the account only is credited to capital reserve
account.

SOME IMPORTANT RAYS

Visible rays
It is the most familiar form of electromagnetic waves. It is the part of the spectrum that is detected by the human eye. It runs a wavelength range of about 700 – 400 nm. Visible light emitted or reflected from objects around us provides us information about the world. Our eyes are sensitive to this range of
wavelengths. Different animals are sensitive to different range of wavelengths. For example, snakes can detect infrared waves, and the ‘visible’ range of many insects extends well into the utraviolet.

Ultraviolet rays
It covers wavelengths ranging from about 400 nm down to 0.6 nm. Ultraviolet (UV) radiation is produced by special lamps and very hot bodies. The sun is an important source of ultraviolet light. But fortunately, most of it is absorbed in the ozone layer in the atmosphere at an altitude of about 40 – 50 km. UV light in large quantitieshas harmful effects on humans. Exposure to UV radiation induces the
production of more melanin, causing tanning of the skin. UV radiation is absorbed by ordinary glass. Hence, one cannot get tanned or sunburn through glass windows.
Welders wear special glass goggles or face masks with glass windows to protect their eyes from large amount of UV produced by welding arcs. Due to its shorter wavelengths, UV radiations can be focussed into very narrow beams for high precision applications such as LASIK (Laserassisted in situ keratomileusis) eye surgery. UV lamps are used to kill germs in water purifiers.
Ozone layer in the atmosphere plays a protective role, and hence its depletion by chlorofluorocarbons (CFCs) gas (such as freon) is a matter of international concern.


X-rays
Beyond the UV region of the electromagnetic spectrum lies the X-ray region. We are familiar with X-rays because of its medical applications. It One common way to generate X-rays is to bombard a metal
target by high energy electrons. X-rays are used as a diagnostic tool in medicine and as a treatment for certain forms of cancer. Because X-rays damage or destroy living tissues and organisms, care must be taken to avoid unnecessary or over exposure.

Gamma rays
They lie in the upper frequency range of the electromagnetic spectrum. This high frequency radiation is produced in nuclear reactions and also emitted by radioactive nuclei. They are used in medicine to destroy cancer cells.

Infrared waves

Infrared waves are produced by hot bodies and molecules. This band lies adjacent to the low-frequency or long-wave length end of the visible spectrum. Infrared waves are sometimes referred to as heat waves. This is because water molecules present in most materials readily absorb infrared waves (many other molecules, for example, CO2, NH3, also absorb infrared waves). After absorption, their thermal motion increases, that is, they heat up and heat their surroundings. Infrared lamps are used in physical therapy. Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the greenhouse effect. Incoming visible light (which passes relatively easily through the atmosphere) is absorbed by the earth’s surface and reradiated as infrared (longer wavelength) radiations. This radiation is trapped by greenhouse gases such as carbon dioxide and water vapour. Infrared detectors are used in Earth satellites, both for military purposes and to observe growth of crops. Electronic devices (for example semiconductor light emitting diodes) also emit infrared and are widely used in the remote switches of household electronic systems such as TV sets, video recorders and hi-fi systems.

MICROWAVE OVEN

The spectrum of electromagnetic radiation contains a part known as microwaves. These waves have frequency and energy smaller than visible light and wavelength larger than it. What is the principle of a microwave oven and how does it work?

Our objective is to cook food or warm it up. All food items such as fruit, vegetables, meat, cereals, etc., contain water as a constituent. Now, what does it mean when we say that a certain object has become warmer? When the temperature of a body rises, the energy of the random motion of atoms and molecules increases and the molecules travel or vibrate or rotate with higher energies. The frequency of rotation of water molecules is about 300 crore hertz, which is 3 gigahertz (GHz). If water receives microwaves of this frequency, its molecules absorb this radiation, which is equivalent to heating up water. These molecules share this energy with neighbouring food molecules, heating up the food.

One should use porcelain vessels and not metal containers in a microwave oven because of the danger of getting a shock from accumulated electric charges. Metals may also melt from heating. The porcelain container remains unaffected and cool, because its large molecules vibrate and rotate with much smaller frequencies, and thus cannot absorb microwaves. Hence, they do not get heated up.

Thus, the basic principle of a microwave oven is to generate microwave radiation of appropriate frequency in the working space of the oven where we keep food. This way energy is not wasted in heating up the vessel. In the conventional heating method, the vessel on the burner gets heated first, and then the food inside gets heated because of transfer of energy from the vessel. In the microwave oven, on the other hand, energy is directly delivered to water molecules which is shared by the entire food.

Radio waves

Radio waves are produced by the accelerated motion of charges in conducting wires. They are used in radio and television communication systems. They are generally in the frequency range from 500 kHz to about 1000 MHz. The AM (amplitude modulated) band is from 530 kHz to 1710 kHz. Higher frequencies upto 54 MHz are used for short wave bands. TV waves range from 54 MHz to 890 MHz. The FM (frequency modulated) radio band extends from 88 MHz to 108 MHz. Cellular phones use radio waves to transmit voice communication in the ultrahigh frequency (UHF) band.

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Heinrich Rudolf Hertz (1857 – 1894)

German physicist who was the first to broadcast and receive radio waves. He produced electromagnetic waves, sent them through space, and measured their wavelength and speed. He showed that the nature of their vibration, reflection and refraction was the same as that of light and heat waves, establishing their identity for the first time. He also pioneered research on discharge of electricity through gases, and discovered the photoelectric effect.

James Clerk Maxwell (1831 – 1879)

 Born in Edinburgh, Scotland, was among the greatest physicists of the nineteenth century. He derived the thermal velocity distribution of molecules in a gas and was among the first to obtain reliable estimates of molecular parameters from measurable quantities like viscosity, etc. Maxwell’s greatest acheivement was the unification of the laws of electricity and magnetism (discovered by Coulomb, Oersted, Ampere and Faraday) into a consistent set of equations now called Maxwell’s equations. From these he arrived at the most important conclusion that light is an electromagnetic wave. Interestingly, Maxwell did not agree with the idea (strongly suggested by the Faraday’s laws of electrolysis) that electricity was particulate in nature.

George Westinghouse (1846 – 1914)

A leading proponent of the use of alternating current over direct current. Thus, he came into conflict with Thomas Alva Edison, an advocate of direct current. Westinghouse was convinced that the technology of alternating current was the key to the electrical future. He founded the famous Company named after him and enlisted the services of Nicola Tesla and other inventors in the development of alternating current motors and apparatus for the transmission of high tension current, pioneering in large scale lighting.

Nicola Tesla (1836 – 1943)

 Yugoslov scientist, inventor and genius. He conceived the idea of the rotating magnetic field, which is the basis of practically all alternating current machinery, and which helped usher in the age of electric power. He also invented among other things the induction motor, the polyphase system of ac power, and the high frequency induction coil (the Tesla coil) used in radio and television sets and other electronic equipment. The SI unit of magnetic field is named in his honour.

MIGRATION OF BIRDS

The migratory pattern of birds is one of the mysteries in the field of biology, and indeed all of science. For example, every winter birds from Siberia fly unerringly to water spots in the Indian subcontinent. There has been a suggestion that electromagnetic induction may provide a clue to these migratory patterns. The earth’s magnetic field has existed throughout evolutionary history. It would be of great benefit to migratory birds to use this field to determine the direction. As far as we know birds contain no ferromagnetic material. So electromagnetic induction seems to be the only reasonable mechanism to determine direction.

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ELECTROMAGNETIC DAMPING

Take two hollow thin cylindrical pipes of equal internal diameters made of aluminium and PVC, respectively. Fix them vertically with clamps on retort stands. Take a small cylinderical magnet having diameter slightly smaller than the inner diameter of the pipes and drop it through each pipe in such a way that the magnet does not touch the sides of the pipes during its fall. You will observe that the magnet dropped through the PVC pipe takes the same time to come out of the pipe as it would take when dropped through the same height without the pipe. Note the time it takes to come out of the pipe in each case. You will see that the magnet takes much longer time in the case of aluminium pipe. Why is it so? It is due to the eddy currents that are generated in the aluminium pipe which oppose the change in magnetic flux, i.e., the motion of the magnet. The retarding force due to the eddy currents inhibits the motion of the magnet. Such phenomena are referred to as electromagnetic damping. Note that eddy currents are not generated in PVC pipe as its material is an insulator whereas aluminium is a conductor.

Michael Faraday [1791– 1867]

 Faraday made numerous contributions to science, viz., the discovery of electromagnetic induction, the laws of electrolysis, benzene, and the fact that the plane of polarisation is rotated in an electric field. He is also credited with the invention of the electric motor, the electric generator and the transformer. He is widely regarded as the greatest experimental scientist of the nineteenth century.

Josheph Henry [1797 – 1878]

American experimental physicist professor at Princeton University and first director of the Smithsonian Institution. He made important improvements in electromagnets by winding coils of insulated wire around iron pole pieces and invented an electromagnetic motor and a new, efficient telegraph. He discoverd self-induction and investigated how currents in one circuit induce currents in another.