What is the principle of photo-chromatic glasses?

Photo-chromatic glasses become dark (activated) when kept under bright light especially when the wavelength of the incident light is in the range of 320-400 nm(nanometres).Darkened glasses get bleached when kept in the dark or under light of longer wavelenghts, 550-650 nm.Both these processes occur simultaneously during daylight and the glass's transparency depends on the predominant reaction taking place in it.
                     These processes are based on the possibility to split and recombine silver and chloride ions in silver chloride using light of different wavelenghts.It is the same principle which is used in photography also. However, in photography, the chlorine and silver ions are separated and not allowed to recombine. In photochromatic glasses, the chloride ions cannot diffuse far away from the silver ions as they are held tightly in a glass matrix. Hence when the 'activating energy' is withdrawn, they recombine to form silver halide. The speed(or rate) of the reaction depends on the doping level of the halide with a catalyst(cooper).
                   Choice of the halides, crystals' size (usually 40-100 Angstroms), concentration, glass type and sensitising dopants are all factors that decide the final behaviour of photochromatic glasses used in light-control, displays, memory applications and optical data processing.

In what way are spatial sound, wide sound and surround sound different from stereo sound?

Let's look at at the way a home music system work.The standard format for home music systems (or FM radio or even television) is the two-channel sound,which is otherwise known as Stereo sound.It is nothing but the two-channel recording,in which sound is played on speakers on either side of the receiver/listener.In the broader sense,stereo effect just recreates the experience of being present at the event.
          Surround sound refers to multi-channel systems.To be more specific, multi-channel systems designed by 'Dolby Laboratories'.It also refers to home theatre multi-channel audio systems, in which sound originates from multiple directions.
         Spatial sound is very much concerned with the concept of localisation.Humans and animals as well hear sound in three dimensions and the very fact is that the perception of spatial aspects of sound is essential to our survival.That is, Spatial waves or sound are well recognised by person since his ear-body-brain combination correctly decodes waves. Assume you are listening to a recorded sound where there is a lack of sensational ambiance, a separation of the instruments and a perception of context of the performance.
        A keen observation reveals that something is missing here. Yes. The missing stuff happens to the Spatial effect or detail. To quote an example, both Virtual Reality (VR) and High Definition Television(HDTV) require spatial sound reproduction apart from what ordinary stereo can offer.But there remains no proof that no commercially available system can successfully convey the natural spatial hearing experience or effect.
       Wide sound is more or less similar to Surround sound. To be more precise, it's a type of sound that is intermediate between stereo and surround effect. The frequency range lies between that of stereo and surround ones.

How does a compact fluorescent lamp consume less electricity than conventional fluorescent lamps and bulbs?

Fluorescent lamps are based on the phenomenon of gas discharge between two electrodes at the ends of the glass tube.Generally these tubes contain a little mercury in the low-vapour phase.When sufficiently large voltage is appiled between the electrodes,some atoms of the vapour get ionised.
The process of ionisation starts with stray electrons and ions that are generally present in the vapour.The electron-ion pair so formed gets accelerated towards electrodes of opposite electrical polarity,gaining kinetic energy.When they collide neutral mercury atoms,some of them are ionised and some are electronically exicted.Excited atoms release their energy in the form of electromagnetic radiation,part of which is in the visible and in the infrared regions of the spectrum.But it is rich in the visible ultraviolet region.
         A fluorescent light source has the inner surface of its glass tube painted with a material called phosphor.Zinc sulphide is the commonest example of a phosphor.But phosphor used in particle are complex mixtures of the sulphides and phosphates of barium,strontium and rare earth elements.These phosphors have the property of absorbing ultraviolet component of the radiation and re-emitting a major fractrion of the corresponding energy in the form of visible light.This enhances the lamp's efficiency of converting electrical energy into visible light.
         The ordinary fluorescent lamp works with a supply voltage of about 220 volt.Since the start of the discharge process demands a little higher voltage,it also employs a starter and ballast(a choke coil) that together produce the desired voltage.On the other hand, the compact tube works at about 400 volt(constant), which is produced by a transformer arrangement embedded in its base.
         Higher efficiency means low consumption of electrical energy.A filament lamp has the lowest efficiency, because is is based on the fact that a material body heated to a high temerature emits radition of all wavelenghts.This radition is richer in the infrared part of the spectrum and since there is no mechanism of converting this into visible light, it has poor efficiency.The three types of lamps may have a typical efficiency ratio of 8:6:3.

Why does a mushroom shaped cloud form after a nuclear bomb explosion?

When a nuclear weapon explodes,there is a rapid release of a large amount of energy within a small volume.This results in significant increase in temperature and pressure.The temperature may be a few tens of million degrees and pressure a few million times the atmospheric pressure.At this temperature,all the material present in the weapon will be converted into hot compressed gases.
Within a fraction of a millionth of a second of the explosion, the weapon's residues emit large amounts of energy mainly in the form of X-rays.The surrounding atmosphere absorbs this energy.This results in the formation of a blazzing, highly luminous, spherical mass of air and gaseous weapon residue called the fireball.
             Within an extremely short time after the explosion,the fireball from a high yield nuclear weapon will be about 130 meters across increasing to about 1700 meters in ten seconds.The fireball expands rapidly engulfing the surround air.
             The ball of hot air is less dense than the surrounding air.It rises swiftly like a hot air balloon.This rising column pulls up debris of the weapon,dust and moisture along with it forming cloud.As it moves up,it cools gradually and reaches about 10km where the atmosphere is extremely stable.The ball of air mass moving up does not have enough energy to penetrate this stable layer.It flattens out.As the relatively warmer layers at the bottom push up,the top layer spread laterally and equally in all directions and the cooler denser layer descend at he edges,giving a distint mushroom shape.
    

Why are all the planets in the universe spherical in shape?

Dip a finger into a bowl of water and then take it out.Now watch the drop of water as it trickles down the finger and drops down. You will notice that the drop of water acquires a spherical shape.Place a drop of mercury on a smooth surface.It attains a spherical shape,this phenomena is due to the cohesive force (force of attraction between the molecules of same element) which brings the molecule closer.
               But then why does it take a spherical shape, why not a cubic one? This is because, out of all multidimensional geometric figures, sphere has the least surface area. Thus all particles try their best to attain a spherical shape in order to reduce their surface area. It is for the same reason that when you pour any liquid in space they attain a spherical shape. But this is not the case with solids since their molecules are compactly packed and cannot be displaced. When a new star is born the gas clouds around it condenses   to form planets. The dense gas passes through three states, the gaseous state , the molten state and finally the rigid solid state. When a planet is in the first two states it attains a spherical structure due to the cohesive force as mentioned in the illustration. Later the molten planet solidifies into a rigid planet like Earth.

Why solar eclipse should not be viewed with naked eyes?

One should not see the Sun during eclipse as the sudden change in light intensity may damage the eye.The human eye, as a protective measure, can adjust automatically to varying light conditions-under bright illumination, as during the day, it closes partially and under dark conditions,as in the night,it opens fully.However this process of adjustment takes some time, a few minutes.

As it is dark during a total solar eclipse, the eyes is fully open to let in more light.After totality, as the sun emerges the increase in light intensity is so sudden that it catches the eye unawares.Being very bright it can damage the retina even in few seconds.

Does the sun rotate?

Yes, the sun too rotates about its axis.But unlike the earth, which has rotation period of one day, the sun has a 'differential rotation'.i.e.All the parts of the sun do not have the same period of rotation.The period of rotation near its equator, sun spot zone, and pole are 26.9, 27.3, and 31.1 days.

The sun's enormous core temperature of 15 million degree Kelvin and a surface temeprature of 6,000 degree Kelvin, leaves all its constituents in the state of a high pressure, gaseous  plasma.For the purpose of certain calculations, the top and the bottom ends of the visible sphere of the sun are designated as north and south poles respectively.

Photographs are taken daily and the movements of the spots, filaments and plages are observed for various latitudes and longitudes, for a long period of time.From this, the sidereal rotation period is calculated.The reason behind this phenomenon is still a puzzle to solar physicists.

Why do we have sodium vapour lamp in the streets and not mercury vapour lamp?

White light consists of seven colours-VIBGYOR.During foggy days,air is highly humid and contains lots of tiny water droplets which can act like a prism.So, if white light is used in automobile headlights and street lamps, water droplets will split it into its componet colours, thereby, creating a circular rainbow around each light source.This will affect clarity of vision and lead to acccidents.In order to avoid this effect, a monochromatic(yellow) light source is used.Yellow is chosen because, being in the middle of the visible spectrum, it undergoes medium refraction and medium reflection while passing through a water droplet.Also, it is next only to whilte in brightly illuminating all objects in their original colour.

However, mercury vapour lamps are used in the interiors because, white light is more pleasing to our eyes, and slight reduction of vision due to fog is not of great concern.

What is the difference between a hydrogen and an atom bomb?

An atom bomb is a fission device.Here a heavy atom (like uranium) is split into two or more lighter atoms.In such a nuclear fission process, one or two neutrons are also released from each atom.If these neutrons are captured bythe surrounding heavy atom, further fission takes place leading to further neutron release.In atomic power reactors, this chain reaction is controlled so that the energ released during the reaction can be used beneficially.

But in the case of an atom bomb, the chain reaction is not controlled but left free.This leads to the release of large amount of heat energy in a very short time resulting in a catastrophic explosion.

In a fusin bomb, such as a hydrogen bomb, two or more lighter atoms fuse together to form a heavier atom.Such fusion reactions can take place only at very high temperature, say a few million degrees Celsius.Only at such temperatures can the starting atoms overcome the repulsive forces acting between them.

In this case also, when uncontrolled fusion takes place a large amount of energy is suddenly released resulting in explosion far bigger than an atomic explosion.

It may be noted that the temperature needed to initiate a fusion reaction is normally obtained by a fission reaction.

What is red eye reduction and its function?

Many Compact cameras and some SLR cameras have built-in flash.The flash cannot be detached from these cameras and may result in "red eye" that is,the pupils of a subject's eyes appear red in coloue photographs.

Red-eye occurs when the light from the flash is reflected off the back of the retina.Subjects pupils are dilated and the On-Camera flash actually illuminates the blood vessels in the eye.The only way to avoid this is to close down the pupils i.e.contract the iris by raising the room lights,or using "red eye reduction flash mode".

This feature is available in sophisticated compacts.This mode fires a pre-flash or a bright lamp prior,thereby reducing the affect.In compacts where there is no red-eye reduction feature,the following technique may be employed to reduce the red-eye effect.The flash light may be bounced off the ceiling or wall,before it reaches the subject.

Why should we not sleep north-south?

Researchers at the Chennai Institute of Magnetobiology,say that sleeping in the north-south direction could make one lack a sense of well being at times.According to Dr.Sankaranarayanan,director of the institute,when a man lies with his head towards north in a pulsating magnetic field,his brain's electrical activity is suppressed or damped.Measurements reveal that blood circulation in fingure tips are affected and the balance between neurochemicals is upset.In addition,it gives subjective experiences like headache,confused thinking and lack of a sense of well-being.
     
As opposed to this,he says,if one sleeps east-west,in the pulsed field,the brain's activity is considerably enhanced.Also,the peripheral blood circulation all over the body is enhanced.Hence he feels relaxed and alert.

It is known that the Earth's magnetic field pulses at extremely low frequencies and is typically in the range of human brain's electrical activity.These pulses are not present always but they peak during certain periods generally associated with solar activity.If one sleeps north-south during such activity headache,general discomfort,nausea and confusion may result.On inactive nights,there may not be any change in the body,he says.

How does remote control in TV works?

In earliar days,remote were based on ultrasonics(sound frequency above the audible range of frequencies).The controlling circuitry included a hand held transmitter (that transmits ultrasound) and a TV-based receiver circuit.Electronic filters and stepper motors were used to allow/select certain frequencies and perform various functions depending on the key pressed.
But the  recent remote controls use infra-red(IR) rays and a special binary (0 and 1) coding menhanism.The code,intensity and wavelength of IR wave,help to select different functions.Depending on the key pressed,a signal is sent out by IR source,say,an injection laser diode(ILD).It generates a code in a parallel format.This is converted to a series format by a shift register.This signal is received by photo-sensitive devices such as an avalanche photo diode at the receiver.

Here another shift register is used to convert the code back to a parallel form.This operates a one-of-n decoder,which selects one function from a set of 'n' predefined functions and executes it.

How is information stored in audio and video tapes?

Information is stored in audio/video tapes by magnetizing them.These tapes are actually long,thin plastic films coated with a magnetic material,mainly iron oxide.Likewise,the player has a recording head which consists of a coil of a wire wound around a circular piece of iron with a small gap.Any current passing through the wire would produce a magnetic field around it.Information (voice or image or any data) to be stored is converted into electrical signals (by microphone) amplified and fed to the recorder head.As the current varies in accordance with the image or sound (input signals) to be recorded,it produces a varying magnetic field.When the tape is run through the small gap present in the recording head,the varying magnetic field magnetizes the particles on the tape rearranged their moments in accordance with the variation int he input signal.

To reproduce the signal recorded,the tape is again run past the recording/playing head which senses the magnetic field along the tape.This induces a varying current in the coil.This current is amplified and fed to the speaker or T.V. to reproduce the original message.

What is Global Positioning System (GPS) and how does it work ?

GPS is a system which shows the exact position on the earth, anytime in any weather and anywhere. There are 24 GPS satellites orbiting at 11,000 nautical miles above the earth. They are continuously monitored by ground station located worldwide. The satellites transmit signals that can be detected by anyone with a GPS receiver. Using the receiver one can determine exact position namely longitude, latitude altitude and the time, with greater precision. GPS has 3 parts: the space segment, user segment and the central segment. Space segment consist of 24 satellites as stated before. User segment consist of receivers which we can hold in hand or mount in a car and this gives the exact location on the earth. The control segment consist of ground stations that make sure that the satellites are working properly.

The satellite are equipped with precise clocks that keep accurate time to within 3 nano seconds (3x 10-9 secs). The time signals are transmitted along with their orbital parameters. The receiver detects the time signal and calculate the distance of the satellite. By getting the signals from 3 different satellites and by doing mathematical calculations, the receiver is able to give the exact position where the receiver's located. By getting the information from 4th satellite, it is able to give the time also. 

Thus 4 satellites are required to compute the 4 dimensions x, y, z and time. At any time and at any location always a minimum of 4 satellites will be visible for the receiver. 

Why are satellites always launched from the east coast?

Earth rotates from west to east causing the sun, the moon, stars and other planets rise from the east and set in the west. On the surface of the earth each point is moving eastward with respect to an astronaut in a space. 

Thus if a rocket is launched at a small angle eastward vertically the speed of the earth is added to the speed of the rocket. This reduces the amount of fuel required. If the rocket is inclined along any other any direction, the speed of earth gets subtracted from the speed of the rocket and will necessitate burning of more fuel.

In addition, in case of any failure during the launch of the rocket will fall back to earth. Hence if it is launched from the east coast , the rocket will fall into the sea only. If it is launched from the west coast, in case of failure, the rocket will fall on the land endangering human habitats. Thus choosing eastward inclination is scientific but choice of eastern coast concern safety.

Why is the earthing pin in 3 pin electrical plugs bigger than the other two pins?

The earthing pin in any 3-pin electrical plug is bigger than the other two pins due to the following reasons.

The earth wire starts from the metal body of the appliance and ends in the earth. So it should never come into contact with live wire. In case the earth pin is connected wrongly with the live socket ,the user touching the appliance might receive an electrical shock.The earthing being thicker in the diameter as compared to the other pins,can never enter the live or neutral socket.Thus the appliance can get connected only in proper electrical position.

Secondly,the earthing pin is made longer than the other pins,so that it gets connected the earth terminal first before the other pins(live and neutral) make the contact in their respective sockets.This ensures safety of the user.

In case there is a short circuit,due to lose contact,weak insulation or electrical leak,as soon as the appliance is plugged in,the current from the electrical appliance flows to the earth without harming the user.Hence it is always safe to install thick high tension wires for earthing.

How do microwave ovens cook food?

A micro wave oven cooks not with the heat but with the radiation similar to radar waves.The heat in an ordinary oven first hits the outside of the food and works its way inward.But microwave radiation goes through the food,bounces off the floor or wall of the oven and goes through the food again.The radiation also changes its polarity or its positive-negative direction several billion times a second.


The rapidly oscillating microwave radiation acts on the water in food because of a special property of water.Water molecule also have polarities one made of oxygen atom,which is negative and two atoms which are positive,each water molecule has positive and negative end.


Every water molecule responds to the reversal of micro wave field by reversing itself,twisting back and forth billions of times a second.As the twisting water molecules rub against other molecules,they generate friction,which causes the food to heat up and cook rapidly.

Why are water drops spherical?

Liquid drops tend to be in a state of minimum surface energy which is directly related to the surface area.the force,surface tension,which is trying to hold the droplet together,therefore tries to reduce the surface area of the drop.Mathematically only a sphere has the smallest surface area for a given volume,compared to other geometric shapes.Hence,in the absence of external forces,liquid drops tend to be spherical.

What is ball lightning?

One of the most rare and mysterious forms of lightning is ball lightning.It is a ball of luminosity that usually occurs near the impact point of a flash and moves horizontally at a speed of a few centimetres per second.It can penetrate closed windows ,is usually accompanied by hissing sound and has a life time of several seconds.The colour is quite variable and the ball often ends with an explosion-however,it is not usually destructive.Also called as globe lightning,it occurs at at times of intense electrical activity in the atmosphere.These balls are said to be plasmas.(plasma is completely lonised state of matter,at high temperature,in which positive and negative ions freely move about).However,no theory has so far satisfactorily explained the behaviour of a ball as scientists have not been able to reproduce it in the laboratory.Lightning ball is comparatively rare sight and so next time you see it,take a picture.

How is depth of oceans measured?

Ultrasonic sounds are used to measure the depth of oceans and the principle behind is known as sound navigation and ranging,Sonar.Ultrasonic waves are sent from a transmitter from the surface of the sea from a ship.


The sound waves are reflected by the sea bottom are sensedbe a receiver system and recorded.With the known value of the speed of sound in water,and the time taken by the sound to travel from surface to bottom and back,the depth is measured.