By pragyansharma polavarapu
(A) BEGINNING AT THE VERY BEGINNING
(1) Imagine a sand grain of one millimeter
cube. Scientists say that can contain 1020 atoms . Please realize that 1020= (one
million) x (one million) x (one million) x 100 ! So big is 1020 and so small are the atoms . There are only 92 varieties in atoms in the universe. Hydrogen atom is the smallest atom.
(2) To understand sizes of atoms the unit
called NANOMETER is used. It is one billionth part of a millimeter. The diameter
of Hydrogen atom is about 0.1 nanometer. Other atoms have alo sizes between 0.1
and 0.5 nanometers.
(3) Every atom has a very heavy
central part called nucleus which is like a positive rock fort containing
positive particles called protons and also a few neutral particles called neutrons.
The negative particles the “electrons” --( smallest purest negative electric
particles in universe)-- circle around the nucleus . They are equal in number
to number of protons of the nucleus and so every atom in universe is neutral
electrically. There are only 92
varieties of atoms in entire universe as
already stated. In interiors of stars the temperatures are in range of tens of
millions of degrees. There is also another very fundamental truth. The electron can be understood both as a particle or as a most minute wisp of energy. The
mass-energy equivalence is given by Dr Einstein’s equation E=mc2 !
(4) In every atom in the universe the
weightless electrons revolve millions of times per
second around the positive nucleus in fixed groove-like orbits . All energy – radio
waves, infra-red, heat, light, ultraviolet, x-rays etc--- is born when
electrons jump from outer to inner orbits to release the excess energy. In Hydrogen
nucleus there are no neutrons. The
positive particle proton is about 1840 times heavier than electron the lightest
negative particle.
(5)All these facts became known thanks to (a)Dr Earnest Rutherford (who “surveyed” the insides of atom as
if checking a dark cave with a torch ), (b)Dr Niels Bohr (who often enjoyed long friendly arguments with Dr Albert
Einstein and found that electrons can stay stable when they rotate in certain circular groovy paths around nucleus and ( c )
the great Dr Einstein ,who while playing
violin (perhaps with eyes closed) sitting
in a boat on Lake Geneva , made many world-shaking discoveries.
(B)THE METALS
(1) Metals like iron, copper, aluminum, silver, gold
are solid shining heavy things with a specific metallic shine. Metals are
malleable and ductile and unbreakable . They easily permit electric
current to pass through . To say correctly, they permit a stream of electrons
to pass through.The non-metals in stark contrast easily break and are brittle and do not conduct electricity.
(2)We know that metal objects should
be carefully handled when they are near to
live electric wires. In a metal spoon there are countless billions and billions of atoms and
each atom has many electrons orbiting it. In the billions of metal atoms ,from
their outermost orbits, some electrons jump down like little children playing on steps of their
houses and wander into the endless electron pool. But same or other electrons of
the endless electron pool always jump back
into the outer orbits. They jump into outer orbits of any nearby atoms in millionth of second and keep atoms perfectly neutral. The situation is
like a big pool of negative electrons and atomic
nuclei existing in the electron pool like thousands of
closely existing islands. The negative charges and positive charges are
perfectly equal and balanced and keep
the atoms perfectly neutral.
In
objects other than metals—(element, compound or mixture ,solid,liquid or
gas)--- there is no jumping down of electrons from the outermost orbits of atoms. This jumping down of electrons from outer
orbits of atoms is only in metals. In all other objects all electrons are
tightly bound in their orbits around the nucleus.
In atoms making every material and object we
see , there are countless billions upon
billions upon billions of electrons in orbits around the nuclei . But except in metal atoms the
electrons are tightly bound rotating in prescribed orbits .
(3)
When a metal object is directly put in current circuit ,the billions
of electrons immediately stop their directionless wandering and behave like billions
of soldiers . They “fall in line”
and start marching from negative pole towards the positive pole. Now the electrons are a billion strong army marching towards the positive pole . We
call this the electric current. The “negative charge impulse” of these electrons
moves towards positive pole at
speeds near to 300,000 kilometers per second!
(4)This electron current is also
somewhat similar to water current in garden hose pipe. The dry cell in our torch light or the Leclanche cell in a laboratory is like a powerful water pumping machine .The electric
cell working like a pump maintains a
strong stream of electrons in the wire circuits and lights
up bulbs and turns fans and other electric motors connected in the circuits .
( C )
THE THERMIONIC EFFECT
(1) An interesting phenomenon was noticed
during the early period of development
of incandescent electric bulbs. This is “thermionic effect” which led to development of modern
technologies of electronics, radio/television
and computers. Even before discovery of the
electron in 1897 by Sir JJ Thompson,
the great American electric
engineer and scientist Thomas Alva Edison noticed in 1880 that in the empty space in
the filament lamp there was a kind of “negative charge” spread everywhere. It was concluded
that some kind of negative particles were evolving from burning hot filament . The scientists of those days felt
that the negative particles are some negative ions (charged particles) and
called them “thermions”. After the “electron” was discovered it was understood that the
thermions were only electrons pushed out from the outer orbits of atoms in
the hot metal filament. But the names thermions, thermionic tube remained even
into the transistor era.
(2)
Thomas Edison noticed another fact. Another independent electric circuit was
created in the same vaccum bulb( at the time of manufacture of the bulb). A tiny “plate” of metal was included in the second circuit. When the plate was positive it attracted a stream of
electrons from the hot cathode. But when the plate was put at a negative charge compared to the hot filament, the movement
of stream of electrons from the hot
filament towards the plate stopped . This effect
was like creating an “electric valve” to stop the stream of electrons –just like a water valve stopping water in a water pipe and permitting flow only in one direction. Though it was a casually
noted fact ,this discovery helped the new technology
of computer . This discovery
helped to create tiny sub-microscopic
switching procedures in thermionic valves for switching on /switching off current a million
times each second. Such very fast switching is required to create 01010101
digits in the computer languages doing arithmetic and logic work in “millionth
of second” time units.
(3 )Thermionic tubes have high vaccum inside. The filament becomes very hot glowing at dull red and from it large number of electrons are ejected and hang like
vapour cloud near cathode. The second
electric circuit in the same thermionic bulb manages this stream of electrons
moving from hot cathode towards the anode. It should be noted that all currents
in thermionic tubes are of very low voltages like 2v,3v,5v etc. Thermionic
tubes do not work with high voltages.
(D)THE WONDERS OF THE FIRST THERMIONIC GLASS BULB TRIODES OF 1940S.
(1) A far more important development
is development of the “triode valve” by
fixing a grid like small wire mesh near
to the cathode as a “third electrode”in
the thermionic tube . When the grid was
given a positive charge it vastly increased emission of electrons from
the cathode. The electrons poured through the wire mesh towards the anode plate which was at a higher
positive potential . The current in the main
circuit got vastly amplified . This “amplification property “of triode tubes
gave rise to the vast high-tech industries of electronic music ,commercial radio/TV and computer technology.
(10)(a) In the era of thermionic glass triodes it was discovered
that the triode can amplify the very weak natural radio
waves(electro-magnetic waves) coming from faraway galaxies which are “light
years” distant from earth(countless billions of miles away) . Galaxies are groups of billions of
stars . Each star is equal to a sun like ours. Scientists using sensitive
scientific instruments detected strong bursts of radio waves from distant galaxies.
(b) When we switch on/switch off
current in our houses then also we hear a loud cracking sound in a radio receiver set . This is also due to radio
wave burst at time of switching on/off current.Electro-magnetic energy is
broadcast in form of waves when we switchon/off current switches. These electromagnetic
waves are caught by our radio receiver sets.
(11) The triodes in radio/TV
stations create and broadcast powerful
electromagnetic oscillations(radio waves) for hundreds or thousands of
miles all around. The signals propagate at
unimaginable very high speed -- 300,000
kilometers in a second! These waves travel
hundreds of thousands of miles above earth even into interplanetary and
interstellar space. This is the basis for audio/video two-way link with space
crafts and orbiting space telescopes. The
radio waves were first demonstrated in laboratory by Dr Heinrich
Hertz in 1886. In the
beginning the radio waves were used only for long distance Morse code
telegraphy(dot-dash-dot-dash signaling).
(12) In later years technology of transmission of sound
(voice/misic) over metal wire and technology of amplification by thermionic valves were perfected. Using the triode and other
thermionic valves radio/TV broadcasting stations came up. In radio/TV broadcasting stations fixed
frequency “carrier waves”(licenced by governments) are created . The radio
waves of voice/photo/video are sent mixed with “carrier waves” by
modulating the carrier waves , In our radio/TV receiver sets the signals are
demodulated . nowadays only the digital
form of waves for radio/tv/computer/digital phone are used.
(E)THE GREATEST DISCOVERY—THE SCIENCE
OF ELECTRONIC COMPUTER
(1)
Every electronic computer-(from old ENIAC and EDVAC of 1940s to latest
desktop/laptop/
digital phone)- utilize the triode valve in every logic circuit in
registers and processors like ALU/CPU . In 1940s the triodes were also of thermionic
tube type. But after discovery of transistors ,hundreds and later millions of submicroscopic “transistor triodes” were created in a single
silicon chip of size of a small postage stamp. scientists create “mathematical logic circuits” using
thousands of triodes (millions of triodes in most modern computers) contained
in the tiny silicon chip.
(2) The capability of triodes –to do a million
calculations in one second ---can be understood through a simple example. A
student at the primary school solves a problem 2+3 on the slate, then wipes the
slate,then solves another problem 5+4, then again wipes the slate clean and
goes to next problem and so on. He takes an hour to solve a dozen problems. Computer
too should delete the working steps of a big problem from the “computer window” to provide the
memory space for working steps in the window for solving the next
problem. After solving the second problem ,again a fresh window with memory
space in back ground should be available.
Computer is so mightily powerful that it can solve a million problems on
one second(by providing new windows).
(3) Though far less in computing
power compared to modern computers, even the old computers of 1940s could do hundreds of thousands of problems in
a second. A most perfect plan of computer’s technical plan( “the IAS model” of computer architecture) was
implemented first in computers of 1940s using only the thermionic tubes . “The IAS architecture” is so perfect that its
general plan is used even in the hundreds of millions of most modern computers.
To construct an old computer of 1940s ,about 15000 thermionic tubes had to be used.
(4)
The basic principle of any electronic computer (whether the giant sized ENIAC,EDVAC of 1940s or modern
transitor- based pocket computer) is utilizing the “speed
of flow of electric current” ( 300,000 kilometers per second ) to do
mathematics and perform logic (thinking) operations .We can call this technological
achievement as one of the greatest
discoveries in human history.
(5) In this age of desktop computer/digital
phone/robotics(AI) , there are far more dazzling discoveries in computer
technology than the “fundamentals about the first computers” mentioned above .The
first part of such a study is learning about the IAS model computer architecture invented in 1940 .
The second part is the study of modern transistor-based computer machines based
on TRANSISTOR/MOSFET/LSI /VLSI technologies.
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