Saturday, September 9. 2017Why is ‘pi’ such a unique number?The Greek letter ‘pi’ is a unique number and is defined as the ratio of a circle’s circumference to its diameter. This number is independent of the size of a circle and for all practical purposes its approximate value is taken as 22/7 or 3.1416. In fact, the fraction 22/7 is slightly greater in value than ‘pi’. For many centuries mathematicians have been fascinated by its unique characteristic. The strangest thing about this number is that nobody has been able to calculate its exact value. Computer scientists have now computed pi to over one million decimal places. At one time the scientists tried to prove that ‘pi’ was a fraction. When any fraction is written in a decimal number, the same digits always appear over and over again in a special pattern. If ‘pi’ were a fraction, there would be a repeating pattern to its digits. But strangely enough a repeating pattern in ‘pi’ could not be found. Finally in 1761, a Swiss mathematician named Johann Heinrich Lambert settled the matter once and for all. He proved that pi is not a fraction. Now the question arises what is the significance of ‘pi’ in our daily life? Suppose you have an automobile tyre whose diameter is one metre. If you want to find its circumference, you can find it out by measuring with a tape. Another way of finding the circumference is to multiply the diameter by this strange number ‘pi’. This number is used to calculate the circumference of all the circular objects. The mathematicians are still engaged in research in this direction to see if the digits are arranged in any special way.
Saturday, September 9. 2017What are the contact lenses?
The contact lenses are worn directly on the cornea of the eyes to correct any defects of vision. All the defects that are corrected by regular eye glasses or others that cannot be corrected thus can be rectified by contact lenses. The first contact lenses to be used as an eye aid were made by A.E. Fick in 1887. These early lenses were first made by blowing the glasses and then by grinding and polishing bottoms of glass test tubes. These lenses were not successful and for a long time remained just a subject of academic study. However, concrete progress in this direction was made in 1938 when the plastic (methyl methacrylate) contact lenses were developed. From 1938 to 1950 many lenses were made by taking impressions of the eye and forming the lens on this mould. Such lenses had a fluid under them and covered most of the eye.
After 1950 smaller lenses were used that covered only the cornea which is the front surface of the eye and floated on a layer of tears. In this case it is not necessary to make an impression of the eye as the curvature of the cornea can be measured by optical instruments. Such lenses are usually 7 to 11 millimeters in diameter and 0.1 to 1 mm in thickness and can be worn all day without removing. To fit the contact lenses, the eyes are first tested for the vision defects just as they would be in case of spectacles. Then the radius of curvature of the eye surface is found out by using a device called keratometer. After deciding the diameter and power of the lens, the prescription goes to the manufacturer for making the lens. To make the contact lens the plastic rod is first sawn into sections and then turned on a lathe to make button-shaped tablets known as bonnets. Then they are given the right curvature with the help of machines for obtaining the desired power and then polished finally. The lenses are then examined to see whether they fit the eye well, or not. Finally they are worn on the cornea. With increasing acquaintance these lenses can be worn comfortably by most people for 12 hours at a stretch. Besides being invisible, contact lenses provide a much wider field of vision than the ordinary spectacles. They are more useful in active sports since they are not easily lost or broken and can even be tinted to protect against the sun. But contact lenses are not effective in all cases of eye trouble. They are also expensive and some people find difficulty in wearing them. As the research continues, even smaller and more flexible lenses are being developed in order to make them less irritating to eyes. Soft lenses of hydroxyethyle are used in modern contact lenses. Saturday, September 9. 2017How are different paints made?
Paint is a mixture of one or more coloured powders and a liquid. The coloured powder is called a pigment. The liquid is called a vehicle or binder. The vehicle carries the pigment and allows it to spread over the surface. Many vehicles contain a solvent or thinner. There are basically two types of pigments – prime pigment and inert pigment. Prime pigments give the paint its colour, and inert pigments like calcium carbonate, clay, mica or talc make the paint durable. Vehicles include oils, varnishes, latex and various types of resins. When a vehicle comes in contact with air, it dries and hardens. This makes the pigment bind with the surface.
There are various types of paints in common use today. The paints often used on walls and roofs are oil-based. Such paints serve to protect wood and metals. Latex paints include wall paints and masonry paints. Many masonry paints are produced with substances like polyvinyl acetate or acrylic emulsions. Lacquers are often used to paint the automobiles. It is made up of a solution of resins in a solvent. The solvent dries up after the laquer is put on. Now we also have fire-retardant paints that protect against any likely damage due to fire. Heat resisting paints are used to cover warm and hot surfaces. Then there are cement water paints that add colour to cement surfaces, such as a basement floor. In the metallic paints, aluminium or bronze powder is used as an ingredient. Enamel paints contain small amounts of prime pigments. They are often used in bathrooms and kitchens. Paint is manufactured in the following process in the paint factories. A small amount of the vehicle is put into a large mechanical mixer. Then powdered pigment is slowly added to the vehicle. Thus a heavy paste of these two items is made. Now the paste is put into a grinder to break-up the pigment particles, and scatter them throughout the vehicle. This operation is followed by ‘thinning’ and ‘drying’. Now, the paint is poured until the solution is thin enough for use. Tinting is the next process. A tinter adds a small amount of pigment to give the paint the exact colour and shade desired. The final steps include straining and packaging. The paint is strained through a filter to remove any solid bits, dust or dirt. It is then poured into a filling tank, and finally into metal cans in which it is sold. |
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