Category Science & Technology

How does an automobile engine work?

          An automobile such as a car is an automatic self-propelled vehicle. It runs on a gasoline, diesel or electric engine. Petrol or diesel engines used in automobiles are internal combustion engines. In these engines, fuel burns in the cylinder. In an electric engine, there is a motor and a gear box. It is battery-powered and used for small cars on a limited and experimental basis.

          Petrol engine is used in most automobiles. However, some automobiles even use diesel engines. Diesel engines are heavier and more expensive than gasoline engines, but they last longer and use less refined fuel.

         Both the petrol and diesel engines are four stroke engines. Their construction and working can be understood as follows:

Petrol Engine: It consists of a cylinder containing an air-tight piston. It is connected with the main shaft through a crank by means of a connecting rod. As the piston moves to and fro, its motion is converted into rotational motion of the crank shaft. The cylinder has two valves: one inlet valve and the other, exhaust or outlet valve. Inlet and outlet valves open and close automatically only once in every cycle. Air is mixed with petrol vapour in a carburetor and is made to pass into the cylinder through the inlet valve. The mixture is burnt in the upper portion by means of an electric spark provided by the spark plug. The action of the engine may be explained in four strokes.

          When the engine is made to work at the beginning by external force, the inlet valve opens and the mixture of petrol vapour and air is allowed into the cylinder. This is known as the charging stroke. Now both inlet and outlet valves close and the fuel mixture is compressed. This is known as compression stroke. The spark plug produces an electric spark and causes the mixture to burn. Due to combustion of the fuel, a large amount of heat is produced. This gives rise to heavy pressure and as a result the piston moves. With the movement of the piston the vehicle moves. This is known as the working or power stroke. Finally the exhaust valve opens, but the inlet valve remains closed. Unused gases, left at the end of the working stroke are thrown out. This is known as the exhaust stroke. In this way, one cycle is over. As the process is repeated, the vehicle goes on moving.

          Most automobile engines have four, six or eight cylinders. Most of the engines are in the front and drive the rear wheels. 

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What is a periscope?

         A periscope is a very useful and interesting optical instrument. It enables officers aboard a submerged submarine to observe whatever might be happening on the surface. A submarine’s periscope can move up and down and turn to look in a complete circle. It allows tank commanders to view the battlefield from inside their armoured vehicles. It is therefore, useful in land and sea warfare. Now let us see what exactly a periscope is.

          A periscope is an optical instrument with which a person can see around corners and other obstructions. This instrument is based upon the principle of reflection of light from two parallel mirrors. A simple periscope consists of a long tube bent twice at right angles. Two plane mirrors, parallel to each other, are fixed in such a way, that the reflecting surfaces of the two mirrors make an angle of 45° with the axis of the tube. Rays coming from an object in front of the periscope, after undergoing two successive reflections, reach the eye of the observer thus enabling him to see the object.

         Some sophisticated periscopes also make use of reflecting prisms and magnifying optics, which make distant objects, appear closer. They are also fitted with devices for estimating the range of the target. Objects can be photographed through a periscope.

          Simple periscopes, made of cardboard, are also popular among spectators at parades and sporting events. With its help, they can see above people’s heads!

          Periscopes are also used in industry to observe nuclear reactions and the interiors of special furnaces and other dangerous devices.

          The longest periscope in the world measures 27 m. It is located at the National Reactor Testing in Idaho Falls, Idaho. It is used to view nuclear reactor operations.

How are hard drinks made?

          Wine is probably the first type of hard drink to have come into existence. Archaeological evidence suggests that wine making began in the middle-east over 10,000 years ago, and gradually spread westward to the mediterranean countries and finally into Europe. The ancient Egyptian wall paintings reveal that the art of wine making was known to them long before the Westerners took to it.

          Wine was common in everyday life of the early Greeks and Romans. It also played an important role in their religious ceremonies. The God of wine was called Bacchus by the Romans and Dionysus by the Greeks.

          Wine can be made from a wide range of fruits and vegetables, but the real wine is made from grapes. Grape juice contains water, sugar, fruit acids and many trace elements. The outer grape skin has millions of tiny living organisms, primarily yeasts, including a number of moulds and bacteria, too. 

          The grapes are allowed to ripen until they attain suitable sugar content (18% or more) and acidity. When these grapes are crushed, yeasts come into contact with the juice. This brings about the process of fermentation by which grape juice changes into alcohol and carbon dioxide. During fermentation, grape juice loses its sugar and turns into wine. This wine has 10 to 14% alcohol content. The rest of wine consists of water containing traces of acids, sugar and other substances which give the wine its colour and flavour.

          Another type of hard drink, beer, is known to have been made by the Egyptians and Babylonians at least 6000 years ago and there is evidence that barley, from which it is made, was cultivated in Britain and northern Europe, some 5000 years ago. Europeans knew how to produce a fermented drink from barley. Beer is usually made from barley hops, yeast and sugar by the process of fermentation.

          Pure brandy is made by the distillation of wine made from grape juice. The wine is heated and the alcohol that evaporates out of it is condensed and collected. Apart from alcohol, other substances are also given off during distillation. Some are poisonous substances and are removed.

          Different types of whisky are made from grains such as barley, rye and corn. Rum is made from molasses, syrup obtained from cane sugar. Gin is made from grain or molasses flavoured with juniper berries.

          Major wine-producing areas of the world include France, Germany, Spain, Portugal, Italy and California in the USA. 

How are matches made?

            When a strip of wood, cardboard or waxed paper tipped with a chemical mixture is rubbed against a rough surface, the chemicals burst into a flame and produce fire. The first match was made in 1827 by an English pharmacist John Walker. It was a splint of wood tipped with antimony sulphide, potassium chlorate, gum arabic and starch. The match bursts into flames with a series of small explosions that showered the experimenter with sparks. The first safety match was invented in 1844 by a Swedish chemist Gustave E. Pasch. Let us discuss how matches are made?

            Red phosphorous is the main substance used in the match industry. Matches are mainly of two types: Lucifer or friction matches and Safety matches. 

            Lucifer or friction matches light when rubbed against any rough surface. The match is basically a wood splint or shaft about 8 cm long and 0.3 cm in diameter. It may have a tip of two colours, red and white or blue and white. One-fourth of the wooden strip is first dipped in molten sulphur or paraffin wax. The small white tip is made from the paste of phosphorous trisulphide. Other substances are antimony trisulphide (kindling material), potassium chlorate (supporter of combustion), powder of glass or silica (friction producing substance) and gum or glue (to act as a binder). Red or blue part of the tip does not ignite by rubbing, but burns when the white tip has caught fire. It carries the flame to the rest of the match stick. These matches are made by machines which produce millions of matches per hour.

            Nowadays only safety matches are used. Safety matches can only be ignited by striking them against a special surface. The surface is usually located on the sides of the match box. The tip of the safety match is made from the substances mentioned above except phosphorous trisulphide. Red phosphorous is used as the igniter in place of phosphorous trisulphide. When the head of the match stick moves over the rough surface, the molecules in the head and the surface collide with each other and the head of the match becomes hotter. The substances in the head become hot enough and make the head burst into a flame. These matches generally do not light when struck on any other surface. The chances of such a match stick catching fire accidentally are thus eliminated.

 

How can the temperature of stars be measured?

           We can measure our body temperature with a thermometer. Thermocouples and other devices are used to measure the temperature of furnaces. But how can we measure the temperature of stars?

          The surface temperature of stars is determined by various techniques. The most conventional and fairly accurate estimate can be made by colour alone. Red-coloured stars are cool while blue ones are extremely hot. On the basis of colour, stars have been classified in the table given below.

          A more accurate determination of the temperature is made by the comparison of spectra of stars. Light, which comes from the sun and other stars, is made up of many different wavelengths. It can be separated into different wavelengths by a spectrograph (an instrument used to record spectrum). From the spectroscopic studies, it has been observed that stars are largely composed of hydrogen (about 75% on the average). Next in abundance is helium followed by various other metals. In the cooler stars, some compounds are present but at high temperatures, they disintegrate into atoms. In order to know the temperature, the spectra of stars are recorded. It will be different for different stars, depending upon their temperature.

          Moreover, the intensity of spectral lines, bright or dark, varies with the temperature. It has been found that blue stars have O-type spectra; our sun has G-type spectra and so on. Blue stars emit 20 or more times the radiation per unit area than that of our sun does, whereas a red type may emit as little as 1/20 as much per unit area.

          From these spectra, by measuring and comparing the intensity of different lines and using Wien’s Displacement Law, the temperature may be determined. Intensity of emitted light is plotted against wavelength and the curve is drawn. The temperature of the star is directly proportional to the frequency at which most of its radiation is given off, i.e. to the highest point of the curve. 

                                                                                                                                                                                            

What are the different types of thermometers?

          A thermometer is an instrument used for measuring the temperature of our body or atmosphere. The first thermometer was produced by the Italian scientist, Galileo Galilei. Thermometers help in regulating chemical reactions by controlling temperatures of the solutions. They are used to measure the melting points of different solids, and boiling points of liquids.

          The main types of thermometers are: I. Liquid-in-glass thermometers. II. Bimetallic strip thermometers. III. Electrical thermometers. IV. Gas thermometers. 

Liquid-in-glass thermometers: The most common liquid-in-glass thermometer makes use of mercury or alcohol as thermometric liquid. The thermometer is made up of a glass tube with a narrow bore through it. At the bottom of the glass tube, a small bulb is blown, in which the liquid mercury or alcohol is kept. It is then put in a hot bath, as a result of which some of the liquid is expelled. The thermometer’s range is decided by the temperature of the bath. Finally its upper end is sealed.

          The sealed glass tube is now put in ice to mark the lower fixed point. This indicates the minimum temperature for the thermometer. Then it is put in another hot bath to ascertain the maximum temperature. The distance between the lower fixed point and the upper fixed point is divided into equal parts. When we wish to measure our body temperature, the thermometer is put into contact with the body. The thermometric liquid expands and stops when the temperature of the bulb becomes equal to the temperature of the body. The temperature is then read from the upper point of the liquid in the capillary.

          Clinical thermometers also contain mercury. Meteorologists use ‘maximum’ and ‘minimum’ thermometers to record the highest and lowest temperatures of the day. They contain both mercury and alcohol.

 Bimetallic strip thermometers: A bimetallic strip thermometer consists of a strip of two different metals having different co-efficients of expansion. This means that different metals expand unequally at the same temperature. The two metals used are usually brass and invar. Brass is an alloy of copper and zinc, while invar is an alloy of iron and nickel. The two strips are joined together. When the temperature changes, the two metals expand and contract at different rates. This causes the strip to bend. The strip is attached to a pointer which indicates the temperature. Bimetallic strip thermometers are used in refrigerators for temperature control. They are also used in thermographs. A thermograph records a graph of temperature. Instead of a pointer, a pen is attached to the bimetallic strip which records the temperature on a moving chart which is known as a thermogram. 

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