My Science School

          To the economist, energy is a synonym for fuel; to the scientist, it is one of the fundamental modes of existence, equivalent to and inter-convertible with matter.

           Energy is the basic requirement for doing any kind of work. It is the energy only that moves trains or cars, produces light from a bulb, makes rivers flow etc. Energy exists in eight forms: (i) mechanical energy (ii) heat energy (iii) light energy (iv) electrical energy (v) sound energy (vi) magnetic energy (vii) chemical energy and (viii) atomic or nuclear energy.

          According to the law of conservation of energy it can neither be created nor destroyed. The total energy content of the universe is constant. It means that the total amount of mass energy in the universe or in isolated system forming part of the universe cannot be changed. It can be simply transformed from one form to another. This is known as the “Law of conservation of energy”.

          Now the question arises: what are the different transformations of energy? The motion of, trains, buses, cars and scooters involves the change of heat energy into mechanical energy. The chemical energy associated with petrol, diesel or coal changes into heat energy on burning. In an electric bulb, the electrical energy is converted into heat and light energy. When we speak before the mouthpiece of a telephone, the sound energy changes into electrical energy and at the receiving end the same electrical energy is transformed into sound energy again. Atomic energy is converted into electrical energy in a nuclear power plant. Chemical reactions in our body produce heat energy to keep it warm. This is how the energy transformations take place in our daily life.

 

The moment we switch on an electric bulb in a dark room in the night, the whole room is illuminated with light and all the articles kept there become clearly visible. Do you know how light is produced from the bulb?

The first electric bulb of the world was developed by the American scientist Thomas Edison in the year 1878. In making this bulb, he utilized the principle that light and heat are produced when electricity is passed through wires. Actually the electric bulb converts electrical energy into heat and light energy. Such light sources are called ‘incandescent lamps’. To begin with, a coil of very fine platinum wire was sealed in a glass bulb used by Edison. When the two ends of this coil were connected to the electric supply, it became red hot and started glowing. Lamps made by Edison could not become popular because platinum wires were very costly.

Subsequently, many changes were made in the filament materials used in the electric bulbs. For some time carbon filaments were used Later on, filaments made up of tungsten and tantalum metals came into use. Since the melting points of these metals are very high, filaments made from them do not easily burn out. 

In the modern electric bulb, the coiled tungsten filament is sealed in a glass bulb. Each end of the filament is welded to a thick wire. These thick wires pass through a glass pillar. Two ends of these wires are soldered with contact pads. To prevent the two ends from coming in contact with each other, insulating material is filled in the metal cap. The air inside the glass bulb is removed and filled with a mixture of argon and nitrogen gases. Thus it prevents the evaporation of metal from the filament and protects it from melting. This mixture also increases the efficiency. When electric current flows through the filament, it first becomes red hot and then white. This glowing white filament gives us the light. The power of a bulb is measured in watts.

While handling a bulb, we should not shake it because the filament is likely to break due to the jerks. Once the filament is broken, the bulb becomes useless. While fixing bulbs in their holders, one should keep the relevant switches off to avoid any possibility of electric shocks.

 

               A team of scientists in Chicago, USA, led by the famous physicist Enricho Fermi, first successfully managed to control nuclear fission. Fission, in physics, is the process of splitting of heavy atomic nuclei into two or more fragments. Under his direction, the ‘so called’ atomic pile or reactor was first established in 1942 to release nuclear energy in a controlled way.

               Do you know what nuclear reactors are? These are the key units in nuclear power stations. In other words, a nuclear reactor is a device for producing nuclear energy in a controlled manner where fission takes place. The nuclei of uranium are used as the main fuel to induce the split that releases a large amount of heat energy.

               Broadly, there are three types of reactors - thermal, fast-breeder and fusion. In thermal reactors the efficiency of fission process is increased by slowing down or sending out neutrons in the core by using moderators such as carbon or graphite. They surround the neutron–absorbing rods in the reactor, made out of boron to release heat energy.

               Fast breeding reactors have no moderators. In these cases, neutrons bring about fission and mixtures of plutonium and uranium oxide are used as fuel. While in operation, uranium is converted into plutonium. The plutonium is extracted and reused later as fuel. It is called fast breeder because it produces more plutonium than it consumes. Fast breeder reactors can extract about 60 times the amount of energy from uranium that thermal reactors do.

               Fusion reactors are not yet in commercial production. Instead of splitting heavy atom, they force very light atoms together.

              In all nuclear reactors, there is a coolant system in which ordinary water or gas like carbon dioxide is used. The heat produced in the reactors turns the water or gas into steam that drives generators to produce electricity.

              The advantages of nuclear energy are that it produces a large amount of useful energy from a very small amount of fuel and does not produce gases contributing to the “Green House Effect”. The disadvantages are that the harmful radio-active nuclear waste that it produced is difficult to store and there is always a risk of accident if something goes wrong.

 

          Rust is a brownish red substance that forms on the surfaces of iron and steel materials when they are exposed to damp air. Rust is a hydrated form of iron oxide.

          Rusting occurs when the oxygen in the air unites with iron by a process known as oxidation. It is also called “corrosion”. But rusting is not only a process of oxidation, because the presence of moisture is also necessary to produce the change. The complex rusting process is an electrochemical reaction that is speeded up by the presence of salts and acids. That is why rusting is more severe in coastal regions and industrial areas where the air may contain acidic sulphur dioxide fumes. 

          Rust not only corrodes the surface but also weakens the metal. Small cells are set up in the corroding metal. It occurs mainly at grain boundaries of metals and where it is stressed. A prolonged exposure to moist air causes rusting, in iron materials and holes in iron sheets.

          Rust can be removed by scrubbing the iron or steel or by using grinding abrasives. There are two basic methods to prevent rusting. The iron or steel may be coated with paint, plastic, or a corrosion-resistant metal such as tin or zinc so that oxygen is stopped from reaching the iron or steel beneath. Chemically coated paper wrapped around metal objects also prevents rusting. The metal may also be alloyed with corrosion resistant metals such as nickel and chromium.

               According to the ancient philosophers, every substance was thought to be made up of very small particles. But because of the lack of scientific knowledge they could not prove it through experiments. John Dalton was the first scientist who propounded the atomic theory in 1803. According to his theory, every element is made up of very small particles called atoms. Atom is a Greek word which means “that cannot be cut” (‘A’ means ‘not’ and ‘tom’ means ‘cut’). Atom can neither be created nor destroyed. Atoms of the same element are similar but atoms of different elements are dissimilar. All these arguments of Dalton have been proved wrong by the modern researchers. It is now an established fact that atom is not the smallest particle of matter. In fact, it is made up of still smaller particles.

               The structure of the atom can be compared to our solar system. Like the planets revolving around the sun, the negatively charged electrons revolve around the positively charged nucleus in different orbits. Almost the entire mass of the atom is concentrated in the nucleus. The nucleus is made up of two types of particles called ‘protons’ and ‘neutrons’.

               Protons are positively-charged particles, while neutrons are neutral particles. The mass of the proton is almost equal to the mass of the neutron. Protons and neutrons are held together in the nucleus by short range attractive nuclear forces.

               Electrons revolve around the nucleus in different circular or elliptical orbits. The number of electrons which can go in the first orbit is two, in the second eight, in the third eighteen, in the fourth thirty-two and so on. The electrons in the outermost orbit are called valence electrons. The properties of any element depend upon the number of valence electrons. When energy is given to an atom, the electrons in the outermost orbit absorb it and are excited to the higher orbits. When they fall back to their original orbit, emission or radiation takes place.

               Today it has become possible to split the atom. Atom bomb is the result of this new discovery. Splitting of atom is called ‘nuclear fission’ which is also used for generating electric power in atomic power plants.

 

        In 1905, Albert Einstein, established a relationship between mass and energy. He proposed a formula which is known as the ‘mass-energy relation’. According to this formula if mass ‘m’ is converted into energy then E=mc, where ‘c’ is the velocity of light and E is the energy released. According to this formula the energy available by the conversion of half a pound of matter will be equal to that produced by exploding 7 million tons of dynamite.

          The real importance of the mass-energy relationship was realized by scientists in 1945 when the first atom bomb converting uranium into energy was exploded by USA. 

          On August 6, 1945, the uranium atom bomb was dropped on the Japanese city of Hiroshima. Three days later, another one, a plutonium atom bomb was dropped on Nagasaki. These bombs killed millions of people. Scientists were amazed to discover the power of nuclear energy. Later, on the basis of this formula, the more powerful hydrogen bomb was also developed.

          After seeing the great destructions in Hiroshima and Nagasaki, scientists thought of making use of this energy for peaceful purposes. Nuclear power plants have been developed to generate electricity on the basis of this formula. Heat energy produced in these reactors by the fission of uranium is used for converting water into steam to run turbines, which in turn run the electric generators. These generators produce millions of megawatts of electric power. Einstein’s mass-energy relationship and its subsequent practical applications have proved to be a great boon to mankind. About 1% of energy needs of the world are now met by nuclear energy.

          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. 

           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.

          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.