My Science School

Polaroid photography is a photographic process in which the processing of the exposed film takes place inside the camera and the print is ready within a minute. It is based on a diffusion-transfer process, which makes it possible to produce a film negative and a positive print in one stage. Developed in 1947 by Edwin H. Land, the process makes use of a special film pack which also contains the printing paper and the processing chemicals. The chemical in the form of a jelly is contained in tiny capsules which burst as the film is moved after exposure. The name Polaroid comes from the name of the company with which Land was associated.

In the Polaroid process, after exposure the film passes through a pair of steel rollers in the camera which releases the developing chemicals. The chemicals convert the exposed silver salts on the negative layer into metallic silver. The unexposed silver salts from the film move to the positive emulsion layer on the paper by diffusion. There they are changed into silver, forming a positive image on the print. Colour film used in Polaroid camera has layers of coloured dyes in addition to negative and positive emulsions.

It is a clock which makes use of the piezoelectric properties of quartz. A quartz crystal has a natural frequency of vibration which depends upon its size and shape. If such a crystal is included in an electronic circuit which applies an oscillating electric field to its opposite faces at a frequency very close to its natural frequency, the entire circuit will resonate or vibrate at the natural frequency of the crystal. Moreover, this frequency of vibration will remain constant over considerable time. In a clock or a wrist-watch, this constant frequency of vibration is converted into electric pulses to drive a motor which in turn drives a gear train to operate the hands or alternatively, the pulses activate a digital display.

Quartz clocks are much more accurate than spring or pendulum clocks. They may accumulate an error of a few tens of seconds in one year. They are used in computers and microprocessors.

 

The theory of relativity was put forth by Albert Einstein in two parts. The first part called the special relativity theory was published in 1905. It stipulates that the velocity of light in vacuum is constant irrespective of the relative velocity of the source and the observer. As a consequence, the measurement of length is dependent upon the relative velocities of the measuring rod and the observer.

For example, to a stationary observer on a railway platform, a train moving with a speed approaching that of light appears shrunk lengthwise. At the same time, to a passenger looking through the window on the train, the railway platform and the observer appear shrunk. But, to both the observer on the platform and the train passenger the immediate surroundings appear normal.

The second part of this theory published in 1915 is called the general relativity theory. It states that the gravitational attraction between two objects is not due to an attractive force but because of a curvature produced in space-time continuum by mass. 

SETI is an acronym for Search for Extra Terrestrial Intelligence. The possibility that intelligent life might exist elsewhere in the universe arises from the fact that the universe is made up of billions and billions of galaxies each containing billions of stars. Even if small fractions of this large number of galaxies have planets with conditions suitable for the appearance of life, there could be several million planets with intelligent life capable of communicating with us using radio signals which are the simplest media of communication. Also radio waves are capable of travelling across astronomical distances carrying substantial information.

However, most of the stars are so far away from us that even at the speed of light it will take several tens or hundreds or even thousands of years for a radio signal from a planet of a distant star to reach the Earth. Another problem is, because of the large distance even the strongest signals would have become extremely weak by the time they reach us. But astronomers are hopeful. They are using very large antenna to collect radio signals however weak from alien civilizations. Scientists at the National Aeronautics and Space Administration (NASA) who launched SETI in 1993 are sending out powerful bursts of coded messages to outer space in the hope of getting a response. But it is too early to say if their efforts will bear fruit. 

The solar wind is a stream of charged particles flowing out from the sun’s outer atmosphere or corona. It blows   at speeds of about 400-500 kilometres per second and on an average takes 4-5 days to reach the vicinity of the earth. It consists mainly of elementary particles such as protons and electrons in roughly equal numbers, together with heavier particles such as alpha particles (helium nuclei). Violent events in the sun’s atmosphere such as flares and prominences send bursts of high speed particles singing through the slower moving wind. The sun loses more than a million tonnes of matter per second into the solar wind. This may appear to be alarming, but it is an infinitesimal quantity compared to the mass of the sun and so there is no danger of the fading away of the sun due to solar winds.

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A common term used to cover an entire range of iron-base alloys that are remarkably resistant to rusting and corrosion because of their chromium content. Stainless steel usually contains 70-90 per cent iron, 12-20 per cent chromium and 0.1- 0.7 per cent carbon. A chromium content of more than 10 per cent with a low carbon content makes iron rust-proof. Nickel and molybdenum may also be added to obtain an improved variety of stainless steel.

A sunspot is a relatively cooler region on the surface of the sun. For an observer on earth, sunspots appear as dark patches on the bright face of the sun. The number and size of sunspots on the sun’s surface keep changing. However, their numbers peak once in about eleven years. The peak-period during which the number of sunspots is very high is called the sunspot-maximum.

Sunspots are believed to be caused by the intense magnetic activity at the sun’s surface which prevents the hot-fluid of the star’s interior from rising to the surface. Thus the surface remains ‘cool’ and ‘dark’. When sunspots occur in large numbers, magnetic disturbances such as occurrence of northern lights or disturbances in the transmission of radio-waves are observed on earth.

Superconductivity is a property which enables electricity to flow through a conductor without any loss. Normally, there is some loss of electricity as heat when current flows through a conductor. This is because atoms of the conductor resist the flow of electrons. The resistance, however, depends on the temperature. Thus, cold conductors conduct electricity better than hot conductors. But some conductors when cooled below a certain temperature called critical temperature, let electricity flow through them without any loss. In other words, they become superconductors. The critical temperature at which a material starts superconducting is specific to that material.

The uses for materials capable of superconducting at room temperature are many. For instance, large currents can be carried to very far off places without any transmission loss by using very thin superconductors. Superconductors also make very powerful magnets. Thus, they can be used to propel superfast trains which move floating above the rails. 

Teflon is the trade name of a fluorine containing polymer chemically known as polytetrafluoroethylene, widely used for coating non-stick kitchenware. It is a polymer in which all the hydrogen atoms of polyethylene are replaced by fluorine atoms. Invented in 1938, by the American company Du Pont, it is a tough, milky-white waxy substance which is totally inert to almost all corrosive chemicals. For this reason, it is used for making valves, seals and gaskets in laboratories and chemical plants. It is non-toxic in normal use. It is highly resistant to the effects of heat and has an extremely low coefficient of friction and has anti-stick property which makes it suitable for coating non-stick kitchenware and running surface of skis and electric irons. Furthermore, it is an excellent electrical insulator and is therefore used for wire covering. Water does not wet it; neither does oil make it sticky.

Any sound of frequencies above the limit of human hearing, that is, 20,000 hertz or more, is called ultrasound. Ultrasound or ultrasonic waves are generated by devices called transducers that convert electrical, mechanical, or hydraulic energy into ultrasonic energy. The intense ultrasound waves generated by these devices can pack enough energy to break kidney stones (a process called lithotripsy); destroy harmful tissues in the brain and force dust and grease off delicate metal surfaces. They can cause liquids such as oil and water that normally would not mix to do so.

Ultrasound is also used to measure the wall thickness of pipes; to detect flaws in metal castings, and in sonar devices to locate enemy ships and under-water obstacles. It is used to monitor the development of the fetus, diagnose tumours, gallstones and heart disease. A beam of tiny bursts or pulses of ultrasound is generated by a small probe which is moved over the surface of the body. Each pulse of ultrasound is reflected or absorbed depending on the characteristics of the tissues through which it passes. The probe picks up echoes reflected from the tissues. The echo pattern is analyzed by a computer that produces an image on a TV screen. 

Vaccines are preventive medicines which when introduced into the body protect it from a specific disease-causing agent. These are usually derived from the disease-causing agent itself which may be a microbe like bacteria or virus, or a toxic microbial product called toxoid.

Vaccines stimulate the immune system of the body to produce neutralizing substances called antibodies as soon as the disease-causing agent enters the body. Vaccines that protect against a microbial disease usually contain the live but weakened or the dead microbe itself. Vaccines for some viral diseases are also prepared from parts of the disease-causing viruses. For diseases such as tetanus or cholera which are caused by toxoids, vaccines are made from chemically inactivated toxoids. Vaccines also contain preservative chemicals and substances called adjuvants which make the immune system react faster and more strongly. Familiar vaccines such as DPT given to children are special preparations for protecting against several diseases simultaneously. DPT protects against diphtheria, pertussis (whooping cough) and tetanus.

The word plastics come from the Greek word Plastikos which means ‘to shape’ or ‘able to be moulded’. All plastics are man-made polymers containing repeat units of the same group called monomer. The process by which plastics are made is called polymerization. The starting materials from which plastics are made are obtained from natural gas and crude oil.

The first plastic was made in the 19th century, by a German scientist Friedrik Schonbein. He accidentally produced a highly combustible substance — nitrocellulose by reacting cotton with nitric acid. Since then several others have been made; among them are polythene, polystyrene, polyvinyl chloride (PVC), polypropylene, polyurethane, nylon and polyester. All these plastics have different monomeric units with specific characteristics.

Plastics can be divided into two major groups— thermosetting and thermoplastics— depending upon the way they behave when heated. Thermoplastics such as nylon and polyethylene become soft when heated and harden on cooling and hence can be recycled many times. But thermosetting plastics such as bakelite cannot he softened or melted once they are set.

 

Plastic money refers to the use of instruments like credit cards instead of cash in business transactions. It is called plastic money because credit cards are made of plastic. At present currency notes, cheques made of paper or coins are used to make payments after a purchase. Credit cards can also be used to withdraw cash from automatic teller machines. Some credit cards are used exclusively for paying call charges in public telephone booths. Plastic money also carries information about its holder in coded form which makes it theft-proof. No one, but the holder is able to use the card.

 

The conversion of electromagnetic radiation like sunlight into electricity through absorption by a semiconducting material is known as photovoltaic effect. Devices based on this effect, such as the photovoltaic cell serve as power sources in remote terrestrial locations, satellites and other space applications. These constitute the basic units by which solar energy is converted to usable electric power. Solar power automobiles and aircrafts have also been demonstrated. Photovoltaic cells are used extensively in photographic exposure meters and in light-operated relay systems used in automation.

In the modern photovoltaic cell light falls upon a junction called a barrier layer between two different types of semiconductors, an ‘n-type’ (negative) and ‘p-type’ (positive). This results in the generation of an electric current. The semiconductors are made of glassy selenium, or crystalline or amorphous silicon.

 

The pacemaker is a battery operated electronic device which transmits electrical impulses to the heart to keep it beating in a regular manner.

In a healthy heart the regularity of beating is controlled by a special system of muscles called the sinoatrial node, situated in the right atrium (the right hand upper chamber of heart) which sends out regular impulses to the heart muscle. When this mechanism breaks down and the heart beat becomes irregular (arrhythmia) or even stops (heart block) an artificial pacemaker is used. A pacemaker is usually implanted in the body on the front of the chest, about 5 cm below the middle of the collar-bone.

The electrical impulses produced by the electronic circuit are sent to the heart via the electric wires which are passed into the right ventricle (the right hand lower chamber of heart) via a large vein and the right atrium. The batteries used in pacemaker usually need replacement once in 10-15 years.