Saturday, 15 October 2011

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.

Friday, 14 October 2011

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.

Friday, 1 July 2011

Why are aeroplanes not affected by lightning?

Clouds are made of water droplets and dust in the atmosphere at altitudes of 1 to 16 km.While traveling through air,due to friction,the water droplets get electrically charged.Lightning occurs due to sparking between oppositely charged clouds-a high voltage spark rushes towards the ground(at zero potential) through moisture-filled air.
If any ground based structure is on the path of the spark,the top of that structure is excited to a high electrical potential while its bottom (in contact with the ground) remains at zero potential.This high potentail difference sets a very high current in the structure causing sudden heat generation in the material and destruction.But in flying aeroplanes,there is nothing like a ground point which remains always at zero voltage.

Hence even if hit by a lightning,the plane's entire surface acquires the same high potential and due to lack of potential difference there is no current and hence no destruction.

What constitutes bulllet-proof glass ?

High-strength ceramics such as silicon nitride,dual hardness steel and layers of heavy nylon fabric make a bullet-proof glass impervious to bullets.The hard ceramic stops the bullet abruptly,dissipates its energy as it destroys the first layers of the glass at the point of impact and entangles it in a coarse mesh.

A textile bullet-proof vest is fashioned of 16-24 layers of nylon cloth of heavy weave,the layers stitched together like a quiet.Such vests or full-torso protectors can be worn undetected under regular clothing.A vest of 16 layers will stop regular handgun and sub machine-gun bullets,those of 24 layers will stop the powerful magnum bullets from the same weapons.

Why do birds fly in formation shaped like the alphabet 'V'?Which bird works the hardest in such a formation and why?

The bird in the lead (at the forward point of the 'V' formation ) works the hardest by being the first to 'break through' the air,which offers resistance to its flight.Just as a boat leaves a V-shaped wake of smoother water behind it(actually the lead bird creates a trail of air turbulence that helps lift along the V-shaped direction),and it is a bit easier for the other birds to fly in the wake of the lead bird.

If you watch a V-formation carefully,you'll notice that the lead bird does not stay in that position for a very long and will drop back into the formation,while another,not as tired bird takes the lead,breaking through the air first.

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.

Saturday, 25 June 2011

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.

Friday, 24 June 2011

Why do people feel sleepy while reading?

Feeling sleepy while reading for many is due to the posture in which they read.While reading a person rarely moves,this lack of physical activity causes decreased blood flow to muscles,which results in accumulation of lactic acid(a product of incomplete combustion in the cells).This lactic acid is a highly reducing or oxygen absorbing agent,which quickly reacts with oxygenated blood.This ensures lack of oxygenated blood flowing to the brain,which makes us feel sleepy.

To tackle this problem we must avoid reading in a single stretch,instead its better to take some breaks and indulge in physical activity at short intervals.

Thursday, 23 June 2011

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. 

How does the speed (of vehicles) measuring device used by the traffic work ?

Chronometers are used to determine the speed of the vehicles with a hand held stopwatch. No radar, no loop just a plain and simple digital stop watch, and two points of a known distance apart. Start and stop switches are to be manually actuated when the vehicle crosses the points.

The speed will be displayed instantly. The second method is by using a Piezo Sensors, this method uses set of 3 rubber strips with a specific distance apart are build across the road or buried in the road. The time between comparisons is measured to give the resulting speed of the vehicle. If the speed exceeds the camera associated with the system will photograph the vehicle.

In another method two beams of invisible infrared beams are emitted across the given traffic lane. The elector optic head directs the beams to two retro-reflectors mounted in the road surface.

Every vehicle passing between the electro optic head and the reflectors breaks beams and triggers the unit computer to measure the speed. If a vehicle exceeds speed limit, the high resolution camera photographs the front or rear of the vehicle including its license plate.

In another method, infra red diodes are pulsed at certain frequencies and to create radar beams. This beam is emitted via parabolic reflector at 15 degree spread and directed towards traffic. The emitters are shielded to prevent external interference.

They normally use K band in a frequency 24 GHZ. The associated computer will measure speed and triggers camera to capture the image of erring vehicles.

What is the black box (in planes) made of ? Normally wat does it do ?

Black boxes which usually hold the clues to a plane's crash, are built strong enough to survive bomb blasts, violent impacts and intense fires. They measure approximately 4 by 6 by8 inches and weighs about 30 kg and are kept in a case which can withstand 30 minutes of 1100 degrees C at 50,000 (Btu's) British Thermal Units per square foot per hour.

They are actually orange in color and a very high quality heat resistant paint is used, so that they can be spotted easily even at dimly lit crash sites. They are always placed in the tail end of the flight.

The black box records voice and flight data. The cockpit voice recorder continuously collects data and retains a record of the most recent 30  minutes, the conversation between the pilot and the Ground Control Room.

The flight data recorder keeps a record of the most recent 25 hours of a plane's operating data, including altitude, air speed, vertical acceleration and heading.
Flight data are recorded either by magnetic tape or in solid-state memory. Modern data recorders can long more than 200 different parameters and transmit data either 64 times or 128 times a second. Thus when recovered from the airplane crash sites the black box helps to reconstruct a clear picture of the crash.

Monday, 20 June 2011

How does a cell phone work?

In normal telephone exchange system,a pair of wires extend each telephone instrument to the telephone exchange.

Normally,copper conductors are used to give loop to indicate the exchange that the telephone handset had been lifted to making a call or receiving a call.In advanced country s, Optical Fiber is also used for extending the loop.

When you make a call to your friend who is connected to another exchange,the digits are send to the  exchange to which you are connected,in the form of pulses (break and make of loop) or frequencies.

The originating exchange analysis these digits and establishes a path to the terminating exchange where your friend is connected .Over this path,signals(some of the digits dialed by you and other technical information)are send in form of bits or frequencies.

The terminating exchange analyzes and marks your friend's line and if it is free, a ring is sent to him and ring back tone is sent to you. When the call is answered, metering takes place.

In the cell phone system, there is no permanent wire connection between the instrument and the mobile telephone exchange. The connection between the instrument and the mobile exchange is established via intermediate station called base station (BS) where a transmitting tower is erected. The connectivity between the mobile exchange and the BS may be the wire and between BS and cell phone is radio channel.

The connection between the mobile exchange and another mobile exchange and public telephone exchange is by wire.

Cell phone are technically called mobile station (MS) and its telephone exchange is called Mobile Switching Centre (MSC). The radio channel for both-way voice and control channel for controlling are established between BS and MS  when required only.

A town or an area is divided into smaller areas called cells.At the center of the cell,there exist a Base Station(BS).When the MS moves inside the cell,the signals including voice will be strong.When you use a cellphone to talk to your friend with conventional phone,you will be connected to the BS over a both way radio channel.From BS to MSC over a copper cable or Optic Fibre cable,from MSC to another exchange and further to your friend over a copper cable.

As you are moving and when you enter into another cell,old BS reports to MSC that you have left the cell and your signals are weak.Immediately ,the MSC order all other Base Stations to search for a newcomer (as far as other cells are concerned ,you are newcomer).

The BS which is very near to you reports to MSC that it has found a new comer with strong signals.The MSC orders the old BS to hand off (you) to new BS. Handing off is done in less than 400 milliseconds. But you do not feel any disturbance in your conversation. You may cross many cells during your long conversation without knowing that so many hands off had taken place. Each cell phone is associated with a unique identity stored in subscriber identity module (SIM). This identity is sent to MSC through BS when "send" button is pressed. 

The MSC analyzes this and validates as to whether cell phone is authorized to make a call. If yes , the call will be put through. When there is any incoming call to the MS, first it is received by the MSC. MSC analyzes the received information that contains the MS number also. This number is paged in all cells. If the MS is kept power on, a page response is received on the control channel from the MS.A voice channel is allotted by MSC. BS and MS are ordered to tune to that channel. Once tuned through connection information is returned to the caller who gets ring-back tone. Ringing is initiated in the MS. When the MS answers, conversation can start and metering starts in MSC. 

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 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 times. According to Dr. Sankarnnarayanan, 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. Measurement reveal that blood circulation in finger 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 oppose 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 range of human brain's electrical activity. These pulses are not present always but they peak during certain time periods generally associated with the solar activity. If one sleeps north-south during such activity headache, nausea and confusion may result. On inactive nights, there may not be any change in the body, he says. This is true for animals also as they are more sensitive to such changes.

Sunday, 19 June 2011

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.

Why do thin glass tumbler break when filled with very hot water?

Glass tumbler break due to the difference in thermal expansion of their inner and outer surfaces.Glass is known as a bad conductor of heat.Hence when the tumbler is suddenly filled with hot water,the inner layer of the glass gets heated immediately as it comes into contact with hot liquid.But the outer layer remains at a lower temperature for some more time as the heat is conducted through the glass only slowly.

As a result,the inner layer tends to expand more than the outer layer.This leads to cracking.Thick-walled tumblers and tumblers made of special quality glass withstand such cracking to a certain extent.

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.

Is it true that a red flag agitates a bull?

It is generally believed that anything red makes a bull angry and causes it to attack.Therefore,the bull fighter has to have a bright red cape and use a red cloth.The truth is that if the bull fighter had any other coloured cloth he would be able to accomplish the same reaction from the bull.Bulls are colour blind.Many experiments were conducted  where they used white cloth and got the bulls to behave in the same way as with the red cloth.

                           The reason is the movement of the cap and not the colour of the cloth brings about the reaction in the bull.Anything waved in front of a bull would excite it.

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.

Saturday, 18 June 2011

How does carbon change into diamond?

Carbon changes into diamond and graphite in the depths of the earth under high pressure and temperature.The process might have taken millions of years.A French scientist,Moissan,verified this theory by experiment.He heated carbon(as charcoal) and iron together in an electric furnace at 3,500 degrees celcius.Carbon dissolved in the molten iron and the mass was cooled suddenly by dipping in water.Then it was put in acid.The iron dissolved and the residue was found to contain a few very small diamonds (less than one millimetre in size) and some graphite .These results were confirmed by others too.Today diamonds are mass-produced by this method.

Artificial diamonds have the same structure,density and hardness as natural diamonds,but are very small.They are also opaque to x rays.Hence they are used mostly for making hard-edged cutting tools and dies and for cutting and polishing natural diamonds,and not for making ornaments.