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Old Saturday, May 30, 2009
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Default Some general questions related to EDS

How is the light produced when an object is burnt?

A chemical reaction is a simple rearrangement of atoms leading to formation of newer substances(products). Hence, to favour the rearrangement,breaking of bonds in the reactants and making of bonds between atoms in the products occur.
Due to this in every chemical reaction there is involvement of energy (liberation or absorption depending on the bond energies of the elements in the reactant and the products). The energy involved may be light, heat or electrical energy.
All combustions (burning) are chemical reactions of a fuel with oxygen in which carbon-hydrogen and oxygen-oxygen bonds are broken in the reactants (except hydrogen) and carbon-oxygen and hydrogen-oxygen bonds are formed in the formation of the products.
The bond energies of these atoms are in such a way that the energy liberated is always more than the energy consumed for the breaking of bonds. The net energy is liberated in the form of both light and heat.


Why is fire hot?

Chemical reactions can be either exothermic(heat liberation) or endothermic (heat absorption). Oxidation reactions are exothermic and reduction reactions are endothermic. Combustion is an oxidation reaction and hence is exothermic.
All liquid,solid and gaseous fuels contain any one of the three combustibles constituents viz, carbon, hydrogen ans sulphur. When a fuel is burnt the heat liberated makes the products of combustion hot. The products of combustion are carbon dioxide, water vapour ans sulphur dioxide. Along with these, the unused oxygen in the atmospheric air supplied for combustion and also the entire quantity of nitrogen which is the major constituent in the air are also heated. That is why fire is hot.


How does one control the movement of hot air balloons?

Hot air balloons rise ito the sky because of the fundamental property of the hot air filled in them; air when heated becomes lighter (less denser) than the surrounding cold air. The balloon does not have controls such as accelerator, steering or brake. It is driven by breeze and so there is no control over the flight path. Ascending is by heating the air with the help of burners suspended beneath it. As a result, the balloon rises to find its equilibrium with the surrounding air. Descending is by releasing the hot air from the balloon. Hot air balloon enthusiasts venture out after studying the weather and making sure there are no strong winds.


Why do two great tastes sometimes not taste great together?

Among the five tastes, salty, sweet and umami (meaty or savory) are appetitive, driving us toward essential nutrients, whereas bitter and sour are aversive, alerting us to potentially harmful substances. Mixing the aversive with the appetitive sends conflicting information to the brain, and confusion is what the senses are trying to avoid as they supply you with useful, lifesaving information. This mixed signal is why you reject food that has gone off. You do not want to eat a blend of the good and the bad.
Yet consider the phrase “sugaring the pill”: pills are medicine and as such are poisonous in large quantities. They thus taste bitter but can be made more palatable by a camouflaging sugar coating. Similarly, coffee can be improved for people who are sensitive to bitterness by masking its sharpness with cream or sugar.
As adults, we can override these warnings and acquire tastes for coffee, olives or strong cheese. But you will confound your senses if you mix a formerly aversive taste with an appetitive one. (Care for some pickles and cocoa?) There can be delight in the confusion, however: sweet and sour is a popular choice in Chinese cuisine.


What is Nucelar Winter?

Nuclear explosions trigger a horrendous chain reaction. The instantaneous outcome is the thermal and blast effect annihilating everything in and around the area. The mushrooming cloud due to the explosion rises high into the stratosphere, spreading out vast quantities of soot and radioactive debris. Some of the debris fall back to the ground as rain out. The soot and other particles suspended in the atmosphere would block sunlight and lower the global temperatures steeply to subzero levels, ushering in wintery conditions over the planet. This sequence of events has been termed as "Nuclear Winter". As a consequence, photosynthesis would stop leading to the destruction of all green plants.
Subsequently oxygen regeneration would cease and carbondioxide would accumulate. Earth's radiation balance and heat budget would get altered leading to drastic changes in the global circulation pattern. the seasonal monsoons and tropiacl rains may disappear. the duration and extent of the nuclear winter scenario would depend on the location, season and intensity of the explosion.


Why are fishes not able to survive in distilled water?

If the fish is in distilled water, there is an osmotic flow of water from outside the fish to the inside because the salinity of the fish body is higher than that of water. Thus there is danger of dilution of the body fluids of the fish or at worst that of being blown out if the fish is to be in distilled water for a very long period of time.


Diamond is a good thermal conductor. But it is an excellent electrical insulator. How?
Diamond crystal is a three-dimensional network of carbon atoms. All carbon atoms in the network are strongly bonded by carbon-carbon covalent bonds.
Therefore diamond crystal has a highly symmetric cubic structure. The carbon atoms in diamond are precisely aligned. Thus diamond is an ideal crystal. Atoms in the crystal lattices in solids vibrate.
These vibrations, called the atomic vibrations facilitate thermal conduction (transport of heat) in solids. In an ideal crystal, the lattices are so precisely aligned that they do not interact with each other.
Therefore an ideal crystal conducts better than a non-ideal crystal resulting in ideal crystals having good thermal conductivity, which is a measure of heat conduction. Diamond being an ideal crystal is thus a good thermal conductor.
Mobile electrons facilitate electrical conduction - flow of current in solids. There are no free mobile electrons in diamond crystal to ficilitate electrial conduction. Thus diamond is an excellent electrical insulator.


Why do houseflies rub their front legs together?

Housefly (Musca Domestica) is a common insect found in all places. It has a very short life span. Adult houseflies feed on human and animal food and waste materials and often use buildings as shelter.
The housefly is well adapted in structure and behaviour to transmit disease causing organisms from place to place.
The body of a housefly is covered with fine hairs and bristles that readily pick up filth particles.
At the base of each leg there is a cushion-like structure covered with granular hairs.A sticky secretion which excretes from the granular hairs gathers bacteria and other micro organisms which stick to the legs. In order to clean its body and the legs, houseflies rub their legs together. It is estimated that whenever a housefly rubs its legs, lakhs of bacteria are discharged from the legs for each rubbing.
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Old Saturday, May 30, 2009
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How do icebergs form?

Icebergs are blocks of fresh-water ice that break off from glaciers and float out to sea. Glaciers are formed in polar regions where snowfall lasts for centuries, or even millennia, without entirely melting, and is eventually compressed into ice.
In the North Altantic, most icebergs originate from the tidewater glaciers of Western Greenland. Compressed snow becomes firm, a granular snow, transformed eventually by pressure into a dense ice. The weight of the icecap builds, causing the ice to flow as much as 60 feet a day through openings in the coastal mountains. Rising and falling tides cause slabs of ice to break off and form moving "rivers of ice".


How does scratching cure itching sensation?

Very sensitive, rapidly adapting, mechanoreceptive free nerve endings that elicit only the tickle and itch sensation are found almost exclusively in the superficial layers of the skin. This sensation is transmitted by very small type - C nerve fibres. These nerve fibres are unmyelinated fibers with a diameter of 0.5 to 2 microns. These fibres transmit impulses as slowly as 0.5 m/sec, unlike the type - A fibres, which transmit impulses at velocities as great as 120 m/sec.
The process of scratching can relieve itch. This scratch reflex is the important spinal cord reflex found in some animals including man. This reflex is initiated by the itch and tickle sensation. It involves two different functions (1) a position sense that allows the hand to find the exact point of irritation on the surface of the body and (2) a to and fro scratching movement. This scratching removes the irritant and the itch is relieved. Sometimes the scratch is strong enough to elicit pain. The pain signals are believed to suppress the itch signals in the cord by the process of lateral inhibition. This lateral inhibition is by the transmission of sensory signals by the anterolateral system, in contrast to the dorsal column system. The anterolateral system is a cruder type of transmission system than the dorsal column system.


What is meant by ozonised mineral water?

Ozone is a blue gas with a relative molar mass of 48 and molecular formula of O{-3}.
It converts back into oxygen after its oxidising process. This makes it the most eco-friendly treatment known today.
Ozone is the ultimate in disinfection. When drinking water is treated with chlorine (chlorine is a highly carcinogenic chemical), the residual chlorine in water is also consumed along with the water.
On the other hand ozone, having half the life of only about 20 minutes, unreacted ozone reduces to oxygen, leaving no trace of toxicity in water.
The water is free from chlorine. Ozone reacts with impurities such as micro organisms including bacteria, virus, spores, mould and fungi. Chemicals such as chlorine neutralise them.
As ozone destroys all micro organisms and it removes disagreeable odours, the resultant water is absolutely safe, pure, fresh and healthy. Ozonised water is colourless and odourless.
The advantage of the use of ozone in water is that it does not leave a dangerous chemical residue like many conventional treating chemicals.
Ozone generators produce ozone by passing oxygen through an electrical field.
Then the generated ozone is bubbled through the water to be treated in a specially designed vessel to control rate of injection. The amount of ozone to diffuse in water depends on the contamination of water.


What is the difference between dial up and broadband Internet connections?

The fundamental difference between dialup and broadband connections is the manner in which the connection is made from PC to the Internet.
A dialup service connects to the Internet through a phone line with a maximum speed of 56kbps.
Broadband refers to a connection that has capacity to transmit large amount of data at high speed. Presently a connection having download speeds of 256kbps or more is classified as broadband.
Broadband comes in a number of forms - depending how the data is delivered - for example via cable, satellite and most commonly using a telephone line where as a dialup service always connects to the Internet through a phone line.
While using a dialup connection, we need to pay for a local call every time we dial the Internet. In addition phone line is engaged while we are on the Internet. With a broadband connection, phone line (if existing phone line is used) can still be used while using the Internet and both the phone and the Internet work simultaneously and no dialup costs are incurred. Telecommunication systems were originally built to carry analogue signals. In a dial up connection, modems are used to translate digital into analogue signals and communicating with Internet.
However, analogue transmission between the subcriber and the telephone company is a bandwidth bottleneck. Dialup connection speeds make it more difficult to view certain types of media, such as video, and it can take much longer to download and open emial attachments, play online games and so on.
In an broadband system, digital data does not have to be converted into analogue. it uses a different part of the line's frequency spectrum, offers much wider bandwidth 9more lanes) and does not interfere with the use of the line for voice transmission. When connected to the Internet, such a connection allows surfing or downloading much faster than a dial-up connection. Dialup connection users a built-in modem to connect and does not require a special router, whereas broadband requires a special router or modem.
In terms of security for attack, dialup is more secured then broadband, Broadband users need to use a firewall to keep the computer "invisible" to the outside.


Why do eggs become hard on boiling?

Egg contain 67 per cent proteins (in egg white) and 33 per cent fats and proteins (in egg yolk). Egg white protein is mostly albumin (ovalbumin and Conalbumin) All proteins have primary,secondary and tertiary structures.
Tertiary structure of egg white protein is due to hydrophobic interactions and hydrogen bonding. They also contain Cysteine amino acid, which has sulfhydryl group (SH).
These sulfhydryl groups form covalent disulfide bonds and hold 2 distant sections of proteins in close proximity. Disruption of the tertiary structure (or 3 dimensional structure) due to heat, chemicals or acidity is called "denaturation".
When we heat an egg, the, heat breaks the intermolecular forces and the tertiary structure gets broken. The proteins unfold from their nature folded structure and precipitate forming a white solid mass.

Why is standing in boats or double decker buses not allowed, particularly in the upper deck of buses?
On tilting the centre of gravity of the boat or bus is lowered and it is likely to overturn.

When wood burns it crackles. Explain?
Wood contains a complex mixture of gases and tar forming vapors trapped under its surface. These gases and tar vapors escape, making a cracking sound.

Why do stars twinkle?
The light from a star reaches us after refraction as it passes through various layers of air. When the light passes through the earth?s atmosphere, it is made to flicker by the hot and cold ripples of air and it appears as if the stars are twinkling.

Why is it easier to roll a barrel than to pull it?
Because the rolling force of friction is less than the dynamic force of sliding friction.

Why is it recommended to add salt to water while boiling, in cooking?
By addition of salt, the boiled point of water gets raised which helps in cooking sooner.

Why is it the boiling point of sea water more than that of pure water?
Sea water contains salt, and other impurities which cause an elevation in its boiling point.

Why is it easier to spray water to which soap is added?
Addition of soap decreases the surface tension of water. The energy for spraying is directly proportional to surface tension.

Which is more elastic, rubber or steel?
Steel is more elastic for the same stress produced compared with rubber.

Why Does ink leak out of partially filled pen when taken to a higher altitude?
As we go up, the pressure and density of air goes on decreasing. A Partially filled pen leaks when taken to a higher altitude because the pressure of air acting on the ink inside the tube of the pen is greater than the pressure of the air outside.

On the moon, will the weight of a man be less or more than his weight on the earth?
The gravity of the moon is one-sixth that of the earth; hence the weight of a person on the surface of the moon will be one-sixth of his actual weight on earth.

Why does a solid chunk of iron sink in water but float in mercury?
Because the density of iron is more than that of water bus less than that of mercury.
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Old Monday, June 01, 2009
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Why does rain come in drops and not in a continuous stream?

When warm wet air rises, it cools and water vapour condenses to form clouds. A cloud is made of small drops of water or ice crystals, depending on its height and how cold its surrounding air is. Most rain originates in nimbus or in towering cumulonimbus clouds.

To form rain, water vapour needs what's called a condensation nucleus, which can be tiny particles of dust, or pollen, swept up high into the atmosphere. When the condensing droplets that form the cloud get large and heavy enough to overcome the upward pressure of convection, they begin to fall.

Although all clouds contain water, some produce precipitation and others drift away placidly without giving rain. First all the droplets in a cloud are less than 20 micrometer in diameter. In a cloud there are lot hygroscopic particles and normally drops form by absorbing moisture by these particles.

Rain is restricted to drops of water that fall from a cloud. They have a typically diameter of at least 0.5 mm. A raindrop large enough to reach the ground without evaporating contains roughly a million times the water of a cloud droplet (typical diameter is 0.012 mm). No matter what the intensity of rain is the size of the drop rarely exceeds about 5 mm. Larger drops do not survive as the process of surface tension which holds the drop together is exceeded by the frictional drag of air and therefore larger drops break apart into smaller ones.

Raindrops as they descend, initiate a chain reaction, a downward trend of the water droplets, with the larger drops always breaking — a common feature observed when one forcefully disgorge the contents of a glass of water.

Most rainfall begins as snow crystals or other solid forms. Entering the warmer air below the cloud, these ice particles often melt and reach the ground as raindrops.

A raindrop starts falling and then picks up speed due to gravity. When one drop starts falling a wake follows in the cloud. (Wake is a clearance that is normally found behind a speeding boat.) This clearance is convenient for another drop to follow and not exactly in the same path but close to it, says Mr. C. Ranganathan of Tiruchy.

Drops that pick up speed are slowed down by the drag of the surrounding air. Indeed the smallest drop may not fall at all, being suspended or perhaps forced upward by ascending currents of air until they grow large enough to fall. As larger droplets descent, they produce an airstream around them.

The larger the cloud droplet the better the chance of its colliding with a giant droplet. So each drop falls at a different speed as their sizes are different. There are collisions between raindrops. Some collisions cause drops to coalesce, forming a large drop and some cause drops to break into smaller ones. As the number of drops grows the intensity of rain increases.

Collision does not guarantee coalescence. Experiments have indicated that the presence of atmospheric electricity may be the key to what keeps the drops together as they collide. That is when a droplet with a negative charge collides with another with a positive charge their electrical attraction may hold them together.

Rate at which drops fall is size dependent. Giant droplets fall rapidly. Thus drops keep on falling side by side and not in a continuous stream.




Why is the Earth's core hot? What caused it to heat up? Is it still heating, or now cooling?

Scientists estimate that temperature at the Earth's core is about 5538{+0}C.

Much of the heat inside the Earth today comes from elements that were present when the planet was first formed billions of years ago. One theory is that radioactive decay of the primordial elements inside the Earth, U-238, Th-232, and U-235 and their radioactive products generate thermal energy (heat).

A nucleus — the central core of an atom — contains both protons and neutrons. Elements, such as the ones mentioned above, have a fixed number of protons but may exist with various numbers of neutrons.

The sum of the protons and neutrons makes up the mass number of an element. Isotopes of an element have the same chemical properties but different weights (indicated by the mass number). Radioactive elements are isotopes with an unstable nucleus.

The isotopes decay by emitting energetic alpha and beta particles until stability is reached. Alpha particles are the nuclei of ordinary helium atoms, which consist of two protons and two neutrons. Beta particles are electrons or positrons. The half-life of an isotope is the amount of time it takes for half of the atoms to decay into a more stable form.

Within the Earth, the released particles from the elements are slowed by friction through interaction with Earth material, thereby generating heat.

The primordial radioactive elements have half-lives on the order of a billion years. Hence, since the Earth formed, their abundance is decreasing over time as a function of their half-life. Therefore, Earth's core is not heating up, it's cooling down.




Why does an egg (with the shell) burst when cooked in a microwave oven?

Microwave radiation is generated in an electronic tube called a magnetron, and passes along what's called a wave-guide into the oven cavity.

The microwaves are absorbed by foods — a characteristic that make them ideal for cooking. The microwave energy transmitted in a microwave oven is directed toward the centre of the compartment. The highest absorption factor for microwave energy is water. The water absorbs the energy and becomes agitated and this molecular level agitation is the friction that heats up food.

When microwaved, different components in an egg expand at different rates, which can result in the egg exploding. White portion of egg contains a high proportion of water and yolk contains a high proportion of fat. Microwaved eggs can reach temperatures much higher than if they were simply boiled in water at 100 degrees Celsius. At these elevated temperatures, water inside the egg, mostly in the white albumen, vapourises — even as the albumen solidifies. If the pressure inside the egg exceeds the breaking strength of the shell, the egg will explode.

Using a wooden pick or tip of a knife to break the yolk membrane of an unbeaten egg before micro cooking to allow the steam to escape, can help prevent the explosion. Covering cooking containers with a lid, plastic wrap or wax paper encourages even cooking and (if we forget to prick the yolk) helps to confine the explosion.
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Old Tuesday, June 02, 2009
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What makes the earth rotate?
The earth rotates simply because it has not yet stopped moving. The Solar System, and indeed the Galaxy, were formed by the condensation of a rotating mass of gas.
Conservation of angular momentum meant that any bodies formed from the gas would themselves be rotating. As frictional and other forces in space are very small, rotating bodies, including the Earth, slow only very gradually. For the Earth rotating on its axis, there is no force working to counteract the rotation (except the tidal effect of the Moon, but that's working very slowly).


What is the peculiar smell of the earth after the first shower?
A pleasant smell after the first shower is because of a group of filamentous bacteria Actinomycetes found in the soil. They grow well in soil when the conditions are damp and warm.
When the soil is too hot, the bacteria are not able to tolerate the desiccation, so it produces spores as survival strategies. The spores remain invulnerable and are resistant to desiccation and heat. During the rainfall, the spores are taken up in the air by the force of wind and suspended in the air as aerosol. When we breathe the air, which contains spores, we are able to feel the earthy "after the rain smell". Geosmine (dimethyl-9-decalols) is the microbial product found in the spores is responsible for the pleasant smell.


Soaps come in different colors. But why is soap's lather always white in color?
Lather or foam is nothing but a large collection of small soap bubbles. A soap bubble is , in turn, a very thin film of soap solution enclosing some air. Because of the low surface tension of soap solution, the film can stretch and spread and form innumerable bubbles with a very large total surface area.
Due to this, whatever slight tint is present in the thin film of the colored soap solution gets subdued. Although a soap film is more or less transparent, the lather or foam looks white because the light striking this large collection of bubbles gets scattered. That is the reason why all kinds of lather or foam appear white.


How are some insects able to walk on the surface of water?
Water has a see-through film on its top layer that is created by surface tension. That means molecules of water are more likely to cling to other molecules of water than to something else. Some insects have a waxy coating on their body/feet. The surface tension of this coating [20 to 30 ergs/cm{+2}] is much less than water [72 ergs/cm{+2}] and hence water tends to bond to itself rather than wetting the insect's feet (in other words this wax is water proof). Secondly a sufficiently large amount of surface area of insect body is in contact with the water. The heavier the object, the more surface area is necessary to maintain floatation. As insects are very light weight the area of contact with the water surface is enough for it to prevent it from drowning.

Why cannot a petrol fire be extinguished by water?
Water, which is heavier than petrol, slips down permitting the petrol to rise to the surface and continue to burn. Besides, the existing temperature is so high that the water poured on the fire evaporates even before it can extinguish the fire. The latter is true if a small quantity of water is poured.

Why is it easier to swim in the sea than in a river?
The density of sea water is higher; hence the up thrust is more than that of river water.

Why does milk curdle?
Lactose (milk sugar) content of milk undergoes fermentation and changes into lactic acid which on reacting with milk protein (casein) form curd.

Why does water remain cold in an earthen pot?
There are pores in an earthen pot which allow water to percolate to the outer surface. Here evaporation of water takes place thereby producing a cooling effect.

Why are ventilators in a room always made near the roof?
The hot air being lighter in weight tends to rise above and escape from the ventilators at the top. This allows the cool air to come in the room to take its place.

Why does grass gather more dew in nights than metallic objects such as stones?
Grass being a good radiator enables water vapour in the air to condense on it. Moreover, grass gives out water constantly (transpiration) which appears in the form of dew because the air near grass is saturated with water vapour and slows evaporation. Dew is formed on objects which are good radiations and bad conductors.
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Why is fuel used in airplanes different from those used in motor vehicles?

Aviation turbine fuels are used for powering jet and turbo-prop engine aircraft. Kerosene was used to fuel the first turbine engines. Kerosene-type fuel was chosen as having the best combination of properties.

As the primary function of aviation turbine fuel (jet fuel) is to power an aircraft, energy content and combustion quality are key fuel performance properties. Other significant performance properties are stability, lubricity, fluidity, volatility, non-corrosivity, and cleanliness. Besides providing a source of energy, fuel is also used as a hydraulic fluid in engine control systems and as a coolant for certain fuel system components.

However, compared to a kerosene-type fuel, other type fuels like used in motor vehicles were found to have operational disadvantages due to their higher volatility:

Greater losses due to evaporation at high altitudes.

Greater risk of fire during handling on the ground.

Crashes of planes fuelled with wide-cut fuel were less survivable.

Lighter (less dense) fuels, such as gasoline, have higher heating values on a weight basis: whereas heavier (more dense) fuels, like diesel, have higher heating values on a volume basis. Since space is at a premium in most aircraft, the amount of energy contained in a give quantity of fuel is important. A fuel with high volumetric energy content maximises the energy that can be stored in a fixed volume and thus provides the longest flight range.

There are currently two main grades of turbine fuel in use in civil commercial aviation: jet A-1 and jet A, both are kerosene type fuels. There is another grade of jet fuel, jet B which is a wide cut kerosene (a blend of gasoline and kerosene) but it is rarely used except in very cold climates.

Jet A-1 is a kerosene grade of fuel suitable for most turbine engine aircraft. It is produced to a stringent internationally agreed standard, has a flash point above 38 degrees centigrade (100 degrees Fahrenheit) and a freeze point maximum of minus 47 degrees Centigrade.

Jet A is a similar kerosene type of fuel, produced and normally only available in the U.S. It has the same flash point as Jet A-1 but a higher maximum freeze point (minus 40 degrees centigrade).

Jet B is a distillate covering the naphtha and kerosene fractions. It can be used as an alternative to jet A-1 but because it is more difficult to handle (higher flammability), there is only significant demand in very cold climates where its better cold weather performance is important.



How is the speed of a computer measured?

Two important factors that determine the speed of a computer are the amount of data that the Central Processing Unit can process in a given period of time and the CPU's clock speed.

The speed at which a CPU executes instructions is called the clock rate.

Every system contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components. The CPU requires a fixed number of clock ticks to execute each instruction.

The faster the clock, the more instructions the CPU can execute per second. Clock speeds are expressed in megahertz MHz or gigahertz GHz. Mega means million and hertz means times per second, 200 MHz is 200 million times per second (and 200 GHz is 200 billion times per second).

The internal architecture of a CPU has as much to do with a CPU's performance as the clock speed. One common architecture is parallel processing. For example, while an instruction is being executed, the next instruction can be fetched from memory and decoded.

Instruction Prefetching is another idea where the CPU fetches the next instruction beforehand and places it in a queue for the execution unit to use the same.

The overall speed of a computer is also affected by the speed and size of the instruction/data bus. The instruction/data bus is the pathway for data communications between the computer's CPU and the various components in the computer.

The computer's bus has a certain size or width called the data path which is measured in bits and the speed of the bus is measured in MHz.

The larger the bus width and/or the faster the bus speed, the more data that can travel on it in a given amount of time.

Another factor affecting the speed is the size of the primary memory and cache. Increasing the size of the primary memory will speed up the performance if you run several applications at the same time or work with large files and documents. Cache is a small amount (normally less than 1 MegaByte) of high-speed memory residing on or close to the CPU. Cache memory supplies the CPU with the most frequently requested data and instructions.

Finally, effective interfacing of Input-Output devices to the CPU also increases the speed. Systems today use direct memory access (DMA) hardware wherein I/O device acts as a master and transfers large number of data to/from memory without intervention by the CPU.



Why do doctors prescribe some medicines to be taken before and some after food?

When we take a medication, it is absorbed from various parts of our gut — some get absorbed in the stomach, some pass through the stomach into the intestines and get absorbed there.

The most important reason for timing a medication that is taken orally is to maximise its absorption so that more of the medication goes through the stomach into the blood.

Many medicines get absorbed better when food is not present and hence are taken on an empty stomach (an example is the hormone thyroxine which must be taken first thing in the morning). A few actually get absorbed better when food is present — an example of this is the antibiotic azithromycin. Some drugs are taken specifically with or after food because this may reduce the side effects of the drug on the stomach.

For example pain medications and certain antibiotics all can irritate the lining of the stomach and therefore are best taken with or after food. Some drugs work in the wall of the stomach to reduce the absorption of food and this is the desired therapeutic effect — an example of this is the anti-diabetic drug called acarbose. This drug must be taken with the first bite of food. Similarly other oral anti-diabetic drugs and the injection insulin are taken before food because that is when they need to act — just after you eat a meal. The long and short of it is that the timing of a drug has important effects on its absorption, action, potency and even side effects and it is a good idea not to leave the doctor's office without being sure when you should be taking your medicine.
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How do raw fruits become ripe when treated with chemicals?

The ripening signal of a fruit comes from a hormone ethylene. Production of ethylene turns on some genes that are transcribed and translated to produce other enzymes. These enzymes are responsible for the conversion of starch into simple sugar, degradation of chlorophyll and appearance of other new pigments like carotenoids, change in the skin colour and the breakdown of acid, making the fruit taste neutral.

Hardy nature of the skin loosens when pectin is broken-down by an enzyme pectinase. Conversion of larger molecules into smaller volatile substances causes an aromatic odour.

Natural process of fruit ripening is accelerated by using certain chemicals. Here, calcium carbide is used. When carbide is dissolved in water it produces acetylene, an analogue of ethylene, a natural fruit-ripening agent.

The ripening process is accelerated since acetylene imitates ethylene. Since the amount of carbide needed to ripen the immature fruit is more it makes the fruit become more tasteless and toxic. Presence of trace amount of arsenic and phosphorous in carbide makes the healthy fruits poisonous.

One can distinguish the artificially ripenened fruit by the uniform skin colour in fruits like tomato, mango, papaws, etc and in the case of banana, yellow colour fruit with dark green stem.


Why are diesel driven vehicles noisy?

Diesel engines are inherently noisy because of the auto-ignition of the initially formed mixture of fuel-vapour and air, which causes rapid rate of pressure rise producing the characteristic noise. This abnormality is due to the inborn feature of a diesel engine, which uses a high compression ratio to obtain high fuel efficiency and a high compression-temperature for ignition of the fuel injected into the cylinder at high pressure. In a diesel engine, unlike a petrol engine, the air and fuel do not mix outside the engine.

Air is compressed to a high compression ratio leading to high fuel efficiency, and also to a high compression temperature to initiate combustion. They just meet inside the combustion chamber for a brief period, while all the processes of mixture formation like fuel-jet break-up, evaporation and mixing should take place within a short time called ignition delay period. Combustion follows this after the initially formed fuel-air vapour auto-ignites with a noise, forming the sources of ignition (chemical spark plugs if you wish to call) for the bulk of the fuel remaining. Diesel engine can be made less noisy by using common rail high-pressure injection system and electronic control.



What causes milk to rise up when we boil it?

Milk contains 87 per cent water, 4 per cent proteins and 5 per cent lactose (milk sugar). When we boil milk, the fat, sugar, proteins and minerals get separated. Since they are lighter than milk they collect on the surface in the form of cream.

During heating some amount of water gets converted into vapour and the bubbles of water vapour rise to the top but the heat is conducted away by the layer of water and by the fat droplets that have a higher boiling point than water.

The vapour gets trapped in the creamy upper layer. As the milk is heated further the water vapour expands and thick foam is produced on the top.

As the milk is boiled continuously the water, which boils at 100 degrees Centigrade, produces more water vapour and pressure builds up in the boiling milk so that the vapour pressure raises the creamy layer. So the milk pushes the creamy layer out and milk spills out.
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Why does it take a longer time to copy a file to a computer than delete it?

An Operating System (OS) is a program that acts as an intermediary between a user of a computer and the computer hardware.

Depending on the storage device being used, computers can store information in several physical forms. Each device has its own characteristics and physical organization, and hence different views of information are created. To unify all these views of information, a uniform logical view called a file is created.

A file is a contiguous set of data. It is the job of the OS to map this sequence of data into physical devices. The part of the OS responsible for this is the file system.

So the main task of the file system is to free the users of the details of storing of information in the physical devices. That is, when the storage device is changed, from disk to CD for example, the user still sees the same information.

In the most basic form, a file system consists of two distinct parts: a collection of files and a directory structure. The directory structure organizes and provides information about all the files in the system.

Every file has certain attributes like its name, location (its address in the file system), size, access control information (whether the file can be read or written to or only executed etc), type (whether it is just a collection of data or has other special instructions), time, date and user identification.

If file A is to be copied to file B, then first a new file called B is created, next the contents of A are read and finally, this is written to B.

For this to happen, three steps are necessary. First, space must be found for B in the file system. Second, an entry for B must be made in the directory. The directory records the name of B and the location of B in the file system. Third, a request is sent to the OS to read the contents of A.

The OS finds the location information of A from the directory and reads the contents. Now to write to B, the OS again searches the directory for the address of B. Finally the content of A is written onto the space provided for B.

On the other hand if a file deletion is to take place, the process is much simpler. If file A is to be deleted, the OS just searches the directory for the named file.

Having found the entry, the space occupied by A is released so that it can be used by other files and the directory entry is erased.

As can be seen, the operations involved while copying a file are much more than those involved while deleting a file.


How does wheat flour become malleable and elastic when mixed with water?

Basically wheat flour does not contain any malleable or elastic characteristic materials. When water is added to wheat flour, a new product called Gluten is formed by hydration of wheat proteins. It causes the production of dough. Gluten contains water approximately 2/3rd of its weight. It forms about 90 per cent of the total protein of flour. It is stretchable product just like rubber. It also contains small quantity of fat, cellulose and minerals.

Gluten in turn contains protein fragments called Glutenin and Gliadin. These two confer the dough the elastic and malleable properties. When mixed together, as they are in dough, these two proteins form a tangle of strands that trap the gas. While gliadin in gluten confers mellowness and elasticity, the glutenin provides the structure. Greater the amount of gliadin, softer will be the gluten. Gluten is responsible for the rheological properties of dough because it forms the skeleton of the dough. High structured products like bread and bun require stronger quality of gluten while low structured products like biscuits and cakes do not require strong gluten.
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How does a rechargeable battery work? What is the life of such batteries and how are they different from ordinary batteries?

Electrochemical cells and batteries are identified generally as primary and secondary batteries. The primary batteries cannot be easily or effectively re-charged electrically and hence are discharged (used) and discarded. The electrochemical reactions in primary cells are not easily reversible. When the battery delivers current (during use) the active materials undergo changes and the active materials slowly will become inactive because the discharged active materials can't deliver current. In secondary batteries (example., lead-acid) the reactions are said to be reversible because once the battery is used, the inactive materials can be converted back to active materials by re-charging and the battery will be again ready for use.

These systems are also called as `storage batteries'. (example., lead-acid, nickel-cadmium) In the primary category, for example., zn-carbon cells, the anode is zinc and cathode is manganese dioxide. During discharge (when battery in use), the simplified reaction can be written as (the actual electrochemical process is more complicated)

Zn + 2 MnO{-2} ZnO + Mn{-2}O{-3}

Discharge (delivers current)

The discharged products (right hand side) cannot be formed back into original active materials (left hand side) by passing current in an opposite direction (charging). It is said to be `irreversible'

Where as in secondary batteries, for example., lead-acid, the active materials can be formed back after discharge (use) and it will be ready for use again after charge.

Pb + PbO{-2} + 2H{-2}SO{-4}

Technically some primary batteries can be recharged for several cycles but may not deliver full capacity and may have poor charge retention after recharge. Generally the cells are not designed for that type of use. The life of a secondary battery (lead-acid or nickel-cadmium) may vary from 200-1200 cycles (one cycle represents one discharge and charge) depending on its design parameters.



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 a glass tube. Generally these tubes contain a little mercury in the low-pressure vapour phase. When sufficiently large voltage is applied between the electrodes, some atoms of the vapour get ionised.

The process of ionisation usually starts with stray electrons and ions that are generally present in the vapour. The electron-ion pairs so formed get accelerated towards electrodes of opposite electrical polarity, gaining kinetic (speed-dependent) energy.

When they collide neutral mercury atoms, some of them are ionised and some are electronically excited. Excited (higher-energy) 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 invisible 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 phosphors used in practice 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 fraction 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 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.

Working at a higher voltage improves its efficiency of producing electromagnetic radiation. Another factor adding to its efficiency is the phosphor composition, which produces light richer on the violet side of the spectrum. This makes the light of a compact lamp somewhat more bluish than that of the ordinary fluorescent lamp. These newer phosphors are not yet being used in ordinary fluorescent lamps perhaps for cost reasons.

Higher efficiency means low consumption of electrical energy. A filament lamp has the lowest efficiency, because it is based on the fact that a material body heated to a high temperature emits radiation of all wavelengths. This radiation 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.
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How does the camel walk in the desert easily?

The camel is dubbed the `ship of the desert'. It can adapt itself easily to the hot conditions due to various reasons. Its special adaptation features are its hump, long legs, long hair and special eyelids.

The hump enables it to store food. Long hair on its body helps it keep warm in the cold desert nights.

The long legs of the camel are strong and have powerful muscles allowing it to carry heavy loads for long distances. It walks at a medium speed. It has two toes on each foot. A hoof that looks like a toenail grows at the front of each toe. The camel walks on a broad pad that connects its two toes. This cushion like pad spreads when the camel places its foot on the ground.

The pad supports the animal on loose sand in much the same way that a snowshoe helps a person walk on snow. The pad enables the animal to firmly grasp the earth. The toenails protect the feet from damages resulting from a bump. In the camel both legs on the same side rise and fall together. This leg action produces a swaying, rocking motion. Taller animals like the camel snap into a rotary walk more often than short animals.

This helps them to shift the balance on one side of a body while the long legs on the other side are in a suspended phase. In the rotary motion on one side they put both legs forward and on the other side they are both back. Thick, broad sole pads and thick callosities on the joints of the legs and on the chest, upon which it rests in a kneeling position, enable it to withstand the heat of the desert sand. It is also able to close its nostrils against flying dust and its eyes are shielded by eyelashes.

The camel has three eyelids and two layers of eyelashes to protect itself from dust and sun. To protect their eyes, camels have long eyelashes that catch most of the sand when desert winds blow sand on to their eyes.

If sand gets into an eye a camel has a third eyelid to get it out. The extra eyelid moves from side to side and wipes the sand away. As the eyelid is very thin the camel can see through it. So a camel can find its way through a sandstorm with its eyes closed.


How do pharmaceutical companies arrive at expiry dates for medicines?

Most of the drugs used in modern medicine are organic molecules, which have, apart from their pharmacological properties, diverse physical and chemical properties. The utility of a drug depends on the availability of the active molecule in blood circulation for curing or controlling the disease. Due to various factors including the structure of the molecule, the formulation the packing and environmental factors these molecules undergo decomposition and degradation over time.

To determine the period over which the degradation will lead to reduction in the availability of the drug to levels below what is required, studies are conducted under what are called accelerated stability tests.

These tests simulate the long term effects of these factors on the stability of the active drug and the formulation in acute experiments lasting up to 45 days at temperatures of 45 degrees or more and humidity of 70 per cent or more. From the correlative data available, it is possible to predict the stability of the drug over long periods of even up to five years.


How do touch screens work?

Touch screen monitors — where you can use your finger on the computer screen to navigate through the contents — have become more and more commonplace over the past decade, particularly at public information kiosks. A basic touch screen has three main components: a touch sensor, a controller, and a software driver. The touch screen is an input device, so it needs to be combined with a display and a PC to make a complete touch input system.

The Touch Sensor has a textured coating across the glass face. This coating is sensitive to pressure and registers the location of the user's finger when it touches the screen. The controller is a small PC card that connects the touch sensor to the PC. It takes information from the touch sensor and translates it into information that PC can understand. The Software Driver is a software update for the PC system that allows the touchscreen and computer to work together. It tells the computer's operating system how to interpret the touch event information that is sent from the controller.

There are three basic systems that are used to recognise a person's touch — Resistive, Capacitive and Surface acoustic wave.

The resistive system consists of a normal glass panel that is covered with a conductive and a resistive metallic layer. These layers are held apart by spacers, and a scratch-resistant layer is placed on top of the whole set up. An electrical current runs through the two layers while the monitor is operational. When a user touches the screen, the two layers make contact in that spot. The change in electrical field is noted and coordinates of the point of contact are calculated. Once the coordinates are known, a special driver translates the touch into something that the operating system can understand, much as a computer mouse driver translates a mouse's movements into a click or drag.

In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch screen driver software. One advantage of the capacitive system is that it transmits almost 90 per cent of the light from the monitor, whereas the resistive system only transmits about 75 per cent. This gives the capacitive system a much clearer picture than the resistive system.

The surface acoustic wave system uses two transducers (one receiving and one sending) placed along the x and y axes of the monitor's glass plate. Also placed on the glass are reflectors — they reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (both other systems have significant degradation in clarity).

Another area in which the systems differ is which stimuli will register as a touch event. A resistive system registers a touch as long as the two layers make contact, which means that it doesn't matter if you touch it with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object — except hard and small objects like a pen tip.


Does frequent switching on/off of a fluorescent lamp reduce its life?

The life of a fluorescent lamp is essentially determined by life of the cathode filament it uses. A conventional fluorescent lamp employs closely wound coil of tungsten wire as filament. Upon switching on the lamp, electric current passing through the filament will raise the temperature of the filament that in turn will generate thermions (electrons generated by a thermal process). Thermions are necessary to initiate electric-discharge through the column of the fluorescent lamp.

Frequent switching on/off the fluorescent lamp occurs through several cycles of filament heating and cooling. If the cycles of heating and cooling of the filament are too frequent this may result in tremendous loss of oxide coating (at the rate of 10-20 micro-grams/cm{+2} per cycle).

The loss of oxide coating in the cathode filament through rapid on/off (heating/cooling) operations will lead to poor performance of the filament in generating thermions to initiate the discharge process. This in turn will reduce the life of the fluorescent lamp. Life of a conventional fluorescent lamp usually rated for several thousand hours of continuous burning can be halved or made still less, just by frequent switching on/off.
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What is the physics involved with breaking glass with your voice?

Any physical object has frequencies at which they naturally vibrate, known as resonance frequencies. If we flick a crystal wine glass with finger, we will hear a fairly clear tone as the glass vibrates, causing waves of air pressure to emanate out from it, which ear and brain interpret as sound. The sound gradually gets quitter and dies out as the amplitude of the vibrations diminishes due to energy being carried away by the sound waves.

Voice is also a series of air pressure waves, with the pitch related to the frequency of the waves, and the volume related to the amplitude of the waves.

If one can match the pitch of voice to the resonant frequency of the glass the vibrating air will start the glass vibrating too. If this can be done with sufficient volume, the glass will try to move in its vibration farther and faster than the material in the glass is able to move, and the glass will break under the strain.



Why is it dangerous to look at the solar eclipse directly specially at that moment?

In general (during non-eclipse times), you've probably been told not to stare at the sun. This is because the sun simply outputs more power than our eye is designed to handle, and exposing our eye to that kind of power can damage the retina. And in a nutshell, solar eclipses are dangerous because the sun can come out from behind the moon and "surprise you" before you have a chance to look away. And this is actually even worse than when you normally look away from the sun because during the total eclipse, it is dark out, and your pupil therefore dilates so that it can let in enough light to get a good picture. Then, when the sun reappears and starts flooding the area with really bright light, not only are you staring straight at it, but your eye is in a state where it is wide open, and actively trying to let in as much light as possible.



Is a drop of water from a dropper equal in volume to a drop of mercury from the same dropper?

The size of a drop of water and a drop of mercury from the same dropper will be different. Assuming that you've filled the dropper to the same level and squeeze the dropper at the same rate, the size of the drop when it separates from the tip of the dropper and falls will be based primarily on two quantities. The first is the surface tension of the liquid and the second is the density of the liquid.
The higher the density, the more mass you have in the same sized drop.

Assuming you're doing this in a gravity environment, more mass means more weight. Which means that for the same sized drop, mercury, which has a much higher density than water, will weigh significantly more, and will therefore have more force pulling it downwards. Mercury has a density of about 13.6 g/cm3, while water has a density of 1 g/cm3.

Surface tension, in this case, provides a resistance to the downward force of gravity. Water has a much lower surface tension that mercury. Water's surface tension is about 73 dynes/cm which mercury is about 465.

So as we see, mercury is at both an advantage and a disadvantage. It has higher surface tension, which allows it to bead up more which, alone, would allow the formation of a larger drop. On the other hand, it has a higher density, which, alone, would result in a smaller drop. Which of these two factors wins out, one can't say. But the drop sizes will be different, barring a coincidence of epic proportions.



Can two persons in a plane which is traveling at a speed greater than the speed of sound will be able to hear each other?

Two people sitting in supersonic airplane such as the Concorde can easily carry out conversations, without much trouble. This is because the air is at rest inside the cabin. It is being carried forward by the airplane just as the passengers are. Since sound propagates in air, and air is at rest with respect to the speakers, everything will operate just as well as it does in any other room.

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