My Science School

          X-rays are invisible electromagnetic radiations. Their wavelengths are smaller than those of the visible light. They are high-energy rays. That is why they have high penetrating power. They can pass through the flesh of our body. They travel with the speed of light.

          These rays were discovered by a German Scientist, Prof. Wilhelm Conrad Roentgen in 1895. They are sometimes called ‘Roentgen rays’ also. They were called X-rays (X means unknown) because these were not known earlier. For this wonderful discovery, Prof. Roentgen was awarded the first Nobel Prize of Physics in 1901.

          The apparatus used for producing X-rays is called ‘X-ray tube’. This tube is made up of hard glass and is fitted with two electrodes which are connected to high voltage power supply. The electrode connected to the negative terminal is called cathode and the one connected to the positive terminal is called anode. Low pressure is created inside the tube by pumping out air from it. When high voltage is applied between the electrodes, electrons emerge from the cathode and hit the ‘anode’ or the ‘target’. As a result the X-rays come out of the tube.

          X-rays are very useful for us. They can pass through substances like wood, paper, skin, flesh etc. but are absorbed by bones, iron, lead etc. Doctors make use of X-rays to detect the dislocations and fractures of bones. They are also used to examine the diseases of lungs and presence of stones in kidneys and gall-bladder. X-rays are allowed to fall on the body part to be examined and a photograph is taken on the photo film kept behind that part. In this film the portion of bones appears grey. From these X-ray photographs, the areas affected by the disease or defects are located easily.

          X-rays are also used in treating cancer. With the help of these rays, gold and other valuable gems hidden in the body are detected easily. They are also used to detect cracks and bubbles in the iron used for constructing bridges and buildings.

          X-rays have a damaging effect on the body’s cells. That is why a person is not exposed to X-rays quite often. Using soft X-rays, instruments like CAT (Computerized Axil Tomography) scanners have been developed to detect body abnormalities. 

                We all know that in our solar system there are nine planets which always revolve round the sun in elliptical orbits. In addition to these planets, there are many small bodies or irregular lumps of rocks which orbit the sun. These small heavenly bodies are called ‘asteroids’ or ‘planetoids’.

               There are about 100,000 asteroids but majority of them are two small to be seen from the earth. Each asteroid has its own orbit in which it revolves round the sun. The biggest asteroid is ‘Ceres’. It measures 1/800th of the size of the earth. The Italian astronomer Piazzi discovered this asteroid in January 1801. The ‘Vestal’ is the only asteroid visible to the naked eye though it was discovered after “Ceres”. The diameter of these asteroids range from 1 km to 800 kms. The total mass of these asteroids is 1/3000th of that of the earth. Two-thirds of the asteroids revolve in orbits lying between the orbits of Mars and Jupiter. Some asteroids revolve between Mercury and Mars also. The asteroid ‘Incarus’ is one of them. The orbit of the asteroid named ‘Hidalgo’ lies between Mars and Saturn. The asteroids ‘Hermes’ and ‘Eros’ are within a range of a few million kms from the earth.

               Eros is a small asteroid that wanders from the asteroid belt and comes within a range of 25.6 million kms from the earth in every seven years, i.e. closer than any other body in the solar system except the moon. It was discovered by G.Witt, in 1898. A second asteroid belt beyond the orbit of “Pluto” has been assumed by the scientists in their recent studies.

               These bodies appear like saucers under powerful telescopes. Some of them are very bright, while some others are faint. Their sizes have been determined on the basis of their brightness.

               Most of the asteroids are constituted of the same ingredients of which the rocks on the earth are made. Their surface temperatures however differ. Scientists believe that asteroids might have originated when some big planets exploded in space and its small pieces then started revolving round the sun. However, nothing can be said about their origin correctly. 

           The thermos flask is a special kind of bottle in which hot liquids like tea and milk remain hot and cold items like ice, cold water etc. remain cold for a long time. It was invented by Sir James Dewar in 1892. That is why it is called Dewar flask also. It consists of a double-walled glass bottle. These walls are silvered from inner side. The space between the walls is evacuated with the help of a vacuum pump and sealed. This bottle is protected by a metal case. A cork is fitted on its mouth.

          It is interesting to know how this bottle helps in keeping the hot things hot and cold ones cold. Normally a hot substance becomes cold by losing its heat to the surroundings having a lower temperature. Similarly a cold substance becomes hot by absorbing heat from the surroundings having higher temperature. The function of the thermos flask is to prevent the flow of heat to and from the bottle. We know that heat can flow from one place to another by three modes: conduction, convection and radiation. The thermos flask prevents the flow of heat by any of these modes. The flask is made up of glass which is a bad conductor of heat. Hence heat does not flow by conduction. Since there is a vacuum between the walls of the bottle, flow of heat by convection is also ruled out. Due to the silvering of the walls heat is not lost by radiation. As a result, hot things kept in a thermos flask do not become cold and cold ones do not become hot for a long time. 

          Anything that occupies space and possesses mass or inertia is known as matter in one form or another. Iron, gold, silver, water, oxygen etc. all are matter. Of these, metals ordinarily exist in solid, water in liquid and oxygen in gaseous state. But all these materials can exist in any of the three states, namely: solid, liquid or gaseous. Matter is composed of basic units called molecules which themselves are made of smaller units called atoms.

          In solid state the molecules of a substance are very close to each other. The force of attraction between them is very strong. That is why the shape, size and volume of solids are fixed and do not compress easily. In the liquid state, the molecules of matter are not so close to each other and as such the force of attraction between them is comparatively less. As a result, the liquid acquires the shape of the container in which it is kept, but its volume remains constant. In the gaseous state, the molecules remain far apart from each other and there is only a very small force of attraction between them. The result is that neither its shape nor its volume remains constant - it acquires the shape and volume of the-container in which it is kept and can be easily compressed.

          All the substances of the universe can exist in any of the three aforesaid states - solid, liquid or gaseous. For example, water, which is normally in a liquid state, becomes solid on being frozen to ice and comes to gaseous state when it is converted into vapours. Similarly under normal conditions, oxygen is a gas, but by cooling it can be converted into a liquid or solid state.

          In addition to these three states of matter, there is a fourth one called the plasma state. The atoms and molecules of matter are ionized in this state. There are both positive and negative ions present in this condition. The shining material in the fluorescent tubes is the plasma state. And same is the case with ionosphere which reflects the radiowaves. Generally, lowering of temperature brings a substance to solid state and the increase in the temperature to a higher degree brings it to the gaseous state and finally to the plasma state.

           The earth is round, and so are the sun and the moon. Even the planets, their satellites and the stars are also spherical. Do you know why all these heavenly bodies are spherical in shape?

           According to a law of science, every physical system in the universe tries to attain a state of minimum energy for maximum stability. It is an established fact that if a sphere is made from a given volume of any material it will have the least surface area compared to any other form. Consequently the spherical bodies have the minimum surface energy. Substances try to acquire a round form like a football in order to achieve the state of minimum energy, that is, the state of maximum stability. This is why the sun, the moon, the stars, the earth and all other heavenly bodies have a spherical shape.

           The rain drops are also spherical. It is so because the surface of the spherical drops has the minimum energy and maximum stability. Whatever be the process of producing the water drops, they immediately try to acquire a spherical shape.

           Atoms and molecules are also spherical in shape. Even the electrons, protons and neutrons present in the atoms are also spherical.

          You might have observed that every man tries to earn the most with the least effort. Every student tries to secure maximum marks after putting in the minimum labour. Thus we see that the tendency to come to the minimum energy state is found in all the living and non-living bodies. As soon as a substance acquires the minimum energy state, its shape becomes spherical.

 

 

          Whatever we hear with our ears is called ‘sound’. In scientific terms, sound is a kind of disturbance which produces sensations in the ears. Like heat and light, sound is also a form of energy. Do know how sound is produced and how it travels from one place to another?

          A body produces sound when a part or the whole of it vibrates. When we strike a bell, vibrations are produced in it that create sound: If we touch a ringing bell with our hands, we can easily feel the vibrations in it. Whenever a living being speaks, the diaphragm in his throat vibrates. Sound can never be produced without vibrations.

         Whenever a body vibrates, sound waves emanate from it and travel in a medium. When these waves reach our ears we hear the sound. Our ears are sensitive to sounds which are produced by vibrations of frequencies ranging between 20 to 20,000 hertz. Human ears cannot perceive frequencies of less than 20 hertz and more than 20,000 hertz.

          Sound travels from one place to another in the form of waves which need a material medium. They cannot travel in vacuum. This can be proved by a simple experiment.

          Take a glass bottle without bottom and connect it to a vacuum pump. Put a cork on its mouth. Suspend an electric bell inside this bottle. Connect the bell to a battery. It starts ringing and we hear the sound very clearly. Now start evacuating the air from the bottle with the help of the vacuum pump. As the amount of air in the bottle starts decreasing, the intensity of sound also decreases proportionately. When all the air is sucked out of the bottle we do not hear any sound. This experiment proves that a medium is always necessary for the propagation of sound waves.

          The aforesaid facts lead to three conclusions. First, sound is produced by vibrations. Second, sound travels in the form of waves. And third, sound needs a material medium for its propagation. Sound can travel through gases, liquids and solids. It travels fastest in solids, followed by liquids and slowest in gases. It cannot travel in space because there is no material medium present there. That is why astronauts talk to each other with the help of radio sets.

 

          Weather is the day to day changes in the state of the earth’s atmosphere. Everyday, we get weather forecast through newspaper, radio and television. The weather experts predict about the possibility of rain, storm or thunder showers. Do you know how this information is obtained? 

          Scientists have to study many aspects to make predictions about the weather. In fact, weather forecasting is the practical application of the knowledge gained through the study of weather behaviour, termed as meteorology. The weather depends mainly on atmosphere i.e. pressure, wind direction, humidity, ambient temperature, cloud formation, rains, snowfall etc. Weather forecasting is organized nationally by government agencies and is coordinated internationally by the “World Meteorological Organization” (WMO). There are three basic stages; observation, analysis and forecasting. Observation involves round-the-clock weather watching and gathering of meteorological data by land stations, balloon launching and also by using satellites. In analysis, information is coordinated at national centres and plotted in terms of weather maps and charts. Then in forecasting, predictions of future weather pattern are made by the “synoptic method” – in which the forecaster applies his experience of evaluation of the past weather patterns to current situation. Computers at these centres analyze the data collected by different methods. Now a day the use of supercomputers have revolutionized the area of forecasting.

          An instrument named ‘anemometer’ is used to measure the speed and the direction of the wind, whereas another kind of instrument called ‘hygrometer’ is used to measure the humidity present in the air. Rain gauges measure the amount of rainfall, while sunshine recorders measure the duration of the sunshine. ‘Maximum-minimum thermometers’ give information about varying temperatures during the twenty-four hours of a day. The atmospheric pressure is measured with the help of barometers.

          Sudden drop in the atmospheric pressure indicates the possibility of a storm or hurricane. Gradual drop in the pressure indicates the increase in the humidity and as such the possibility of rain. Easterly winds are also indicators of rain. Rise in the atmospheric pressure heralds fine weather.

          Normally if fresh milk is not boiled for sometime it becomes sour. But this does not happen with boiled milk for several hours. Do you know why it is so?

          Fresh milk contains several types of bacteria. When milk comes in contact with air, the number of the bacteria multiplies very fast. These bacteria turn the milk sour. The bacteria come to the milk from three different sources. First, if the cow or the buffalo from which the milk comes is suffering from some disease it might be excreting bacteria in its milk. The tuberculosis germs are transmitted from cattle to man in this way. Secondly, the milkman could have certain infectious disease and might contaminate the milk while milking the cow. Thirdly, the water used to wash the milk pot or the teats of the cow or buffalo may have germs in it. The bacteria transmitted to the milk from any of these three sources grow very fast and spoil the milk.

          Pasteurization is a process for sterilizing milk and other drinks invented by Louis Pasteur (1822-1895) – a French micro-biologist and chemist, for improving storage qualities and to protect them from spoiling. This method is named after him. The milk and butter sold in the market are normally first pasteurized, and then marketed.

          In the process of pasteurization, milk, wine, butter etc. are heated up to a certain temperature and then quickly chilled. This kills the bacteria in them. If milk is heated up to 63° for 30 minutes in between 72°- 85° for 16 seconds and then chilled to 10° or less, the bacteria present in it are destroyed. Pasteurization not only protects the milk from being spoiled but also kills the bacteria of tuberculosis and other diseases. Pasteurized milk can be kept unspoiled for a longer time without boiling. The process does not affect the taste of the milk.

          Nowadays gamma rays and beta rays are also being used for pasteurization. These rays kill the bacteria present in the milk and other drinks. 

          We know that the sunlight consists of all those colours which are seen in a rainbow. These colours are: violet, indigo, blue, green, yellow, orange and red. Light from the sun travels in the form of waves which are known as electromagnetic waves. The different colours of light have different wavelengths. Our eyes are sensitive only to the wavelengths relating to the above seven colours. Apart from the wavelengths of these seven colours, the sunlight consists of radiations of other wavelengths also, but our eyes are not sensitive to them. Rays having wavelengths higher than of red light are called infra-red rays and those lower than violet light are called ultraviolet rays. Both infra-red and ultraviolet rays are not visible to our eyes. 

          Infra-red rays come not only from the sun but from every hot object. Burning wood and coal, electric heater - all produce these rays. Infra-red rays were discovered by the British astronomer Sir William Herschel in 1800. In fact all objects give of infra-red rays according to their temperature. The warmer an object is, the more infra-red rays it gives off. These can be recorded on special type of photographic films made of infra-red sensitive materials. Whenever these rays fall on any material body they produce heat. They are very useful to us.

          Infra-red radiations are being used for the treatment of several diseases. Special types of infra-red lamps are used for treating the pains of muscles and joints - especially for back pain. They are also used for heating rooms in winter.

          Infra-red radiations are being used for the guidance and control of missiles and other ballistic weapons. These radiations are also used for transmitting and receiving invisible signals. Molecular structures are studied with the help of these radiations. Impurities present in the materials can also be detected by these rays. Infra-red absorption spectroscopy is an important analytical tool in organic chemistry.

 

          The number of naturally occurring stable elements on the earth is 92 only. Although scientists have so far discovered 107 elements in all, but 15 of these have been artificially made in the laboratories. These artificial elements are unstable in nature. The atoms of these 92 elements are also of 92 kinds only. Do you know how millions of substances are made from these elements?

          All substances available in the universe are made by the combination of atoms of these 92 elements. The atoms of different elements combine with one another in various proportions and keep on forming countless substances. Some of the important elements are: iron, gold, silver, copper, aluminium, sodium, potassium (metallic elements), oxygen, nitrogen, chlorine, carbon, sulphur (non-metallic elements). All the elements consist of atoms and the atoms of the same elements are alike. Two or more atoms combine with each other to make molecules. For example, two atoms of hydrogen combine with one atom of oxygen to make one molecule of water. Even a very small quantity of water consists of innumerable molecules. Similarly one atom of sodium combines with one atom of chlorine to make one molecule of the common salt sodium chloride. 

Continue reading "How are millions of substances made from only a few elements? "

          Whenever any substance is put in to fire it burns and changes into ash. But asbestos is one such material that does not burn in fire. That is why the fire fighters wear clothes made from asbestos when fighting large fires. In fact their clothes, shoes, gloves, helmets etc. are all made from the fibres of this material.

          Asbestos is a Greek word which means ‘inextinguishable’ or ‘unquenchable’. The invention of this material is not new. The Romans used asbestos sheets 2,000 years ago for wrapping dead bodies in order to preserve them.

          This material is obtained from mines. It is formed by the dissociation of olivine. Olivines are the silicates of calcium and magnesium. Due to certain chemical reactions in the mines, olivine changes into fibres of asbestos. Asbestos obtained from mines is first dried and then its fibres are separated with the help of machines. These fibres are woven into threads and ropes which are then used for making clothes, sheets, mats etc.

          Asbestos is a very useful material. It is used for making fire-proof clothes, paper and as heat-insulator in furnaces. It is also used for making fire proof tiles for buildings. In cold countries, water pipes coated with this material which serve as insulators preventing water from freezing in the pipes.

          It is a bad conductor of both heat and electricity and is least affected by acids and alkalies. It does not burn even at a temperature of 2000°C to 3000°C. Some special varieties of asbestos are now available which do not burn even at 5000°C. This variety is used in research laboratories. The most common mineral of asbestos is chrysotile found in Canada and Russia.

          Canada is credited with 75% of the total world production of asbestos. America manufactures maximum number of items from asbestos though the raw material obtained in this country is only 5%. 

          Pressure cooker is a modern kitchen appliance that can cook almost any type of food in a very short time. It also saves a lot of fuel. Moreover, the nutritional constituents of the food are also not spoilt. Do you know how the pressure cooker helps in fast cooking?

          We know that every liquid boils at a definite temperature at the normal atmospheric pressure. This temperature is called the ‘boiling point’ of the liquid. In the case of water it is 100° C. It is observed that with the increase of pressure, the boiling point of the liquid also increases. Similarly reduction in the pressure lowers its boiling point. It is this phenomenon that prompted the invention of pressure cooker. 

          Pressure cooker is essentially a vessel of stainless steel or an alloy of aluminium. It has a lid fitted with a safety valve at its top to let out the steam in order to maintain the internal pressure within the limit the vessel can bear. A rubber ring is fixed at the junction of the vessel and the lid which does not allow the steam to leak out. A thermally insulated handle is attached to the pressure cooker for handling it. The food to be cooked is put in the vessel along with some water and the lid is closed. When the vessel is heated, the steam so formed increases the pressure inside the vessel. As the pressure increases, the boiling point of water also increases and it reaches up to 130°C. This is why food gets cooked quickly inside the pressure cooker. When the steam pressure inside the cooker increases beyond the required pressure, the control valve is automatically lifted up, allowing the excess steam to escape. Thus the pressure inside is regulated and there is no risk of bursting.

          If there is no hissing or whistling after the cooker has been kept on the oven for a sufficient time, the valve should be slightly shaken to see if the hole below is not choked. Before opening the lid the valve should be slightly lifted up with the help of tongs to allow the steam to escape. 

          Radio waves belong to the family of electromagnetic waves which owe their existence to moving electrons. The existence of radiowaves was first predicted by James Clerk Maxwell in 1860, but it was not until 1887 that Heinrich Hertz succeeded in producing them experimentally. “Wireless” telegraphy was first demonstrated by Sir Oliver Lodge in 1894 and it was Guglielmo Marconi, the Italian scientist, who could first successfully transmit a long distance transmission in 1900 with the help of radiowaves.

          It is through radio waves only that sound from the broadcasting station is able to reach our radios. Their use is also made to transmit a variety of programmes. Radio waves work as the carriers for communication signals. The message is modulated with radio waves and transmitted with the help of a transmitter. The modulated signal is received by the radio receiver and then decoded. Radio waves were also used to keep in contact with the flying planes. With the help of these waves they are properly guided and controlled during flights thus avoiding accidents.

          Radio waves are in fact invisible electromagnetic waves which travel with the speed of light, i.e. at 300,000 km. per second. Satellites and spacecrafts keep in contact with the earth stations with the help of these waves. Live communication with the satellites and astronauts has become possible only due to radio waves. These waves can travel both through the air and the vacuum. They can even travel in water and underground to a distance of a few metres. Communication is established between the ships with the help of these waves. Every ship is equipped with radio transmitters and receivers.

          To study the radio waves originating from the different heavenly bodies, scientists make use of radio telescopes. With the help of these telescopes, it has now become possible to identify the planets and stars which generate the radio waves.

          Radio waves are also used by police. They have the equipments by which they can send and receive messages from moving vehicles. Fire brigades also use of radio waves while providing help in accidents. These waves are also used to control traffic. Today we have the instruments which can measure the speed of a moving vehicle from the control room itself.

          In a nutshell, we can say that the world has shrunk due to these radio waves. 

          We see millions of stars twinkling in the sky during night. They radiate their light in all the directions. Even though they appear very small yet in reality they are very big. Most of the stars are many times bigger than our earth. They look smaller only because of their great distance from the earth. Do you know why the stars twinkle?

          Our earth is surrounded by a thick cover of air known as the atmosphere. There is vacuum beyond the atmosphere. The gases present in the atmosphere are in constant motion. Because of the movement of gases the density of air in the atmosphere is not uniform everywhere. As such the refractive index of air varies from place to place. When the light from a star enters our atmosphere, it gets deviated from its path several times before reaching our eyes because of the changing density and the consequent change in the refractive index of the air.

          The deviation in the path of light in its passage from one medium to another is called ‘refraction’. Because of this refraction, the light reaching our eyes from the star varies. Due to this variation the stars appear to be twinkling.

          Now the question arises: why don’t moon, sun and other planets twinkle like the stars? This is so because compared to the stars, sun, moon and the planets are very near to earth and as such they appear bigger than the stars. Hence the angles subtended by the moon, sun and the planets at our eyes are larger than the angles subtended by the stars. Because of the larger angles, our eyes are not able to detect the deviation in the path of light from the sun, moon and the planets and hence they do not appear to be twinkling. 

          Over the years application of modern technology in the domestic sphere has made our lives more comfortable and easier. Washing machines, vacuum cleaners, microwave ovens etc. are a few examples that meet the demands of the modern society of today. The new gifts of technology especially for household use, always generate a curiosity in us about their working principles. Now let us discuss how does a microwave oven work?

          A microwave oven does not have burning flames or red-hot plates like gas and electric cookers. Its operational mechanism is simple. The user puts the food into a metal box and presses a switch. Inside the box, invisible energy rays bombard the food. 

          The oven gets its name from the rays that cook the food - the rays are called microwaves. Microwaves are part of the spectrum of electromagnetic waves which includes light waves and X-rays. They have wavelengths from about 30cms to one millimetre which places them between the shortest radio waves and infra-red waves. One of their properties is to excite molecules, especially in liquids, and make them vibrate and heat up. For this reason, food with a large proportion of water gets cooked very quickly.

          The source of microwaves in the oven is a magnetron. It is a two-electrode valve for generating high-frequency oscillations. Microwaves generated by the magnetron travel down a metal-duct and are scattered around by a metal fan for a more even cooking. The molecules rub against each other and the friction produces heat. The water then gets heated up and consequently the food gets cooked quickly.

          Microwave ovens are a potentially dangerous source of radiation. For this reason the ovens are metal lined and have strong doors. The oven will not function until the doors are closed thus ensuring safety. Most modern ovens contain small computers that automatically cook the food at the appropriate temperature for the right length of time. Microwave ovens are preferred and widely used in restaurants, hotels etc. where quick service is important.