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.