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NOVEMBER 27, 2012

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It flies on the same principle as the kite does. Two forces to lift and to drag it are caused by the relative velocity of the plane w.r.t wind. The lift can be improved by increasing the relative speed of wind, done by running the plane on the ground initially. As the plane moves forward, air flows over and below the wings. The aeroplane always has a streamlined shape to minimize the resistance of air. The wings are designed in an aerofoil section, leading to a lower pressure on the upper surface of the wing than on the lower surface, which gives rise to a lift, making the plane airborne.




An equipment with a fissionable element and a moderator (such as heavy water or graphite to slow down the speed of neutrons), in which a self sustaining fission process goes on at a controlled speed.




In an atomic reactor, heat energy is produced by the controlled fission of Uranium. A fissionable Uranium atom (mostly enriched Uranium is used, obtained by increasing the proportion of fissionable Uranium from ordinary Uranium) is bombarded with neutrons at a certain speed, producing lighter nuclei of other elements and three neutrons in addition.



Out of these three neutrons so produced, two are made inactive by reducing their speed. The third one is again made to strike another fissionable Uranium nucleus, thereby repeating the process. Out of three neutrons so produced now, two are again deactivated while the third one strikes another Uranium nucleus. This chain reaction goes on at a controlled speed. That is why, this is known as a controlled chain reaction. When such a reaction starts taking place on a self-sustaining basis, the production of power starts. At this stage, the reactor is said to have achieved criticality.



The total mass of the end-products in such a reaction is always lesser than the total amount of initial participants in the reaction, i.e. some amount of mass disappears. This disappeared mass appears in the form of energy according to the well-known Einstein’s mass-energy equivalence equation

                                                                                                                     E= mc2



where E is the total energy produced, m is the mass disappeared in the reaction while c stands for the speed of light. (300000 lakh kilometers/second).



This equation also explains why such a tremendous amount of heat is generated by the disappearance of a small amount of mass. This heat is used to generate steam which in turn drives the turbines. These turbines drive the generator and thus electricity is produced.





The exact opposite of nuclear fission. In case of nuclear fusion, two smaller nuclei fuse with each other, thus producing a bigger nucleus. For example, if you join hydrogen nuclei to produce a helium nucleus, this process will be known as nuclear fusion. But while fission can be done at room temperature, this is not true of fusion. To make fusion possible, one needs a very high temperature, of the order of lakhs of degrees. Now such a temperature is made possible only by conducting a fission reaction. Therefore, a nuclear fusion is always preceded by a fission reaction. The high temperature generated during the fission enables the fusion to take place. The source of energy in this case remains the same, i.e. the mass disappeared in the reaction.




Since such reactions take place at a very high temperature, they are also referred to as thermonuclear reactions. The fusion process is widely used in making hydrogen bombs. Since a fusion bomb is in reality a double bomb (fusion+ fission), it is quite destructive. Such a fusion reaction taking place on the Sun (in which hydrogen nuclei fuse together to create the helium nuclei) has been supplying energy to us for many billion years and will continue to do so for another 4 billion years.




If you could have nuclear fusion at room temperature, it would be referred to as Cold Fusion. Scientists have been trying hard to make it possible, but till now, it remains a science fantasy. Some years back, the University of Utah scientists had reported a major breakthrough in having Cold Fusion, but it turned out to be a hoax. The day it becomes possible, all energy problems of the world will be solved in one go.





The moving pictures on cinema screen are based on the principle of persistence of impression on the retina. The human eye cannot distinguish between two pictures seen in time interval of less than 1/16th of a second. The movie film consists of snapshots taken at intervals of about 1/25th of a second. When these snapshots are projected in quick succession with time intervals less than 1/16th of a second, the retinal images get fused into one another, and the impression of a continuous motion of pictures is obtained. The same is true of all other moving picture phenomena.





A CD offers true reproduction of sound, almost no noise or distortion, unlimited disc life, massive storage space and immunity from dust and minor scratches. All these are realized by the digital encoding of the audio waveform and optical readout of the encoded information. The signal is recorded on the disc as binary code, as a series of Os. and 1s. This is achieved forming pits along a spiral track on a transparent plastic disc, covering this with reflective waves, followed by a protective layer. Light from a laser is focussed onto the pits from below and the reflected light, picked up by a photo-detector, converts the presence or absence of pits into a binary electrical signal.





DAVY’S SAFETY LAMP (Miners’ Safety Lamp) 
Invented by Sir Humphry Davy. It is designed to save the lives of the labourers working in coal mines. It consists of an ordinary lamp, the naked flame of which is surrounded by a wire gauze so that there is no connection between the air inside the lamp and outer atmosphere, except through the gauze. The inflammable gases from the mine enter the gauze and burn inside, giving out a blue flame. The gauze conducts the heat of the flame so well that the temperature outside and near the gauze never reaches the ignition point of the gas.





A dynamo converts mechanical energy into electrical energy. The mechanical energy required is obtained from a gas engine or from steam or water turbine. A generator has a rectangular coil of wire wound on a laminated iron core, called armature. The armature rotates under a strong magnetic field created by an electro-magnet. As the coil rotates, a current is induced in the coil according to Farady's Law of Electromagnetic Induction.





The electric iron has the same working principle as an electric heater i.e. heating effect of electric current.  A resistance coil is wound on porcelain or mica and is placed inside the electric iron. By switching on the current, a large amount of heat is produced due to the large amount of current.





HDTV (High Definition Television)
A TV picture is made of a certain number of horizontal scan lines each having a certain number of perceptible spots. The sharpness of the picture depends on the total number of spots per frame. HDTV has at least twice the resolution of conventional systems as it has at least twice the number of scan lines HDTV requires a larger display and five times the channel capacity of the existing system and a different aspect ratio from conventional the 4 : 3.





The Jet Engine is based on the principle of Newton’s Third Law of Motion. It is best explained by untying an inflated balloon and releasing it into the air. As the air from the balloon is released backwards, the balloon moves forward. In a Jet craft, the fuel burns in the compressed air, hot gases under high pressure are produced, which escape backwards via a fine jet. These escaping gases cause a reaction, which pushes the jet forward.




A jet craft is more economical for long journeys. It can fly at higher altitude and can acquire supersonic speeds i.e., speeds more than that of sound (about 740 m.p.h.). Jumbo Jets or Boeing 747s can carry up to 450 passengers and travel at about 1000 km per hour.





Consists of a metal tube containing three mirrors, inclined at 60o. One end of the tube is closed by a piece of ground glass and the other one by a cap provided with a hole. Small pieces of coloured glass are placed at one end between the ground glass and another glass disc. On looking through the hole, the other end being held towards light, a beautiful pattern formed by multiple reflections will be seen.





CT SCAN (Computerized Tomography)
The conventional X-ray is a flat, two dimensional (2D) image without any depth. Imaging techniques enable us to see the depth of the object (i.e., the third dimension) as well.  A slice of any organ in any orientation can be imaged for examination. These techniques are called Computerized Axial Tomography (tomo means slice).




The basic idea behind computerized tomography is to make a number of observations of the object in question from a number of directions and angles. Several thousand observations are taken and the huge data thus obtained is analyzed by digital computers to yield a 3-dimensional image of the object, any slice of which can be selected and examined. X-Ray Computerized Tomography employs X-Ray for imaging purposes, the patient being scanned by an X-Ray tube which can rotate 360o. In PET (position emission tomography), the patient is administered positron- emitting radioactive substances. Observing the gamma-ray photons emitted from these substances enables us to have a 3-D image of the object.





NMR (Nuclear Magnetic Resonance)
Different from X-ray and PET techniques since it is a spectroscopic technique. It uses radio-frequency waves and combines spectroscopy and imaging. This makes possible non-invasive spectroscopy. Body biochemistry can be studied at any part (slice) of a body organ. Since radio frequency waves used in NMR scanning are less energetic than the X Rays in X-ray CT scanning, NMR is less harmful to body tissues than the latter.





Certain elements, if kept in dark (keeping them in dark is not a pre-condition, they emit rays even otherwise, darkness makes them more visible), emit positively, negatively charged and neutral rays. This phenomenon, discovered by Henry Bacquerel, is referred to as radio-activity. Almost all elements starting from Uranium (Atomic Number 92) upto the end of the periodic table are radio-active in nature. The three types of rays emitted are:



Alpha–rays are + ly charged particles (actually they are helium nuclei)

Beta-rays are negatively charged particles (in reality, they are electrons)

Gamma-rays are electro-magnetic waves of short wavelength with great penetrating ability.



Since radioactive materials decay at a definite and measurable rate, the amount of un-decayed radioactive material can give us an idea of the time elapsed in disintegration. This principle is used in radio-active dating, which is a technique use to determine the age of ancient rocks, tress etc, historical monuments. Mostly, Carbon-12 is used for radio-active dating.





A unit of distance to measure the distance between astronomical bodies. A Light Year is defined as the distance travelled by light in one year (3 lakh kilometers multiplied by seconds in one year).





If a light of a minimum wavelength is made to fall on certain metals, they start emitting a stream of electrons, which, if channelled properly, gives rise to an electric current. This phenomenon is referred to as photo-electric effect. Examples of such metals easily susceptible to this effect include Sodium, Lithium etc. This phenomenon is the basis of photo-voltaic cells used to generate electricity in remote villages. This is a cheap, clean, non-polluting and a virtually inexhaustible source of power.





A ballistic missile is a vehicle which can guide and propel itself in a direction and with a velocity such that it will follow a ballistic trajectory (elliptic path) to a point on earth. A guided missile uses aerodynamic forces under the direction of its guidance system to control its trajectory. Hence guided missiles are used for applications that require trajectories mainly in the earth’s atmosphere. They are used over shorter ranges than ballistic missiles, which are used over continental ranges, and must therefore follow an exo-atmospheric path.




Examples of ballistic missiles are the Intercontinental Ballistic Missiles (ICBMs) and India’s Agni missile while examples of guided missiles INCLUDE Scud missiles and all Indian missiles except Agni.



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