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.

 

          In the beginning, when man made boats, he also used them for the sea voyages. But he did not dare to travel too far because of the fear of losing his way as he did not have any instrument to find directions in the sea. During those days, sea travellers used to find different directions with the help of the sun and the stars. But when the sun and the stars were not visible in a cloudy weather, finding the right direction was very difficult.

          About 1000 B.C., a black stone with peculiar properties was discovered at Magnesia in Asia Minor. It used to attract small iron-pieces. This stone was named as ‘magnet’ since it was discovered in Magnesia. It was observed that a freely suspended magnet always points towards the north and south. It is because the earth itself behaves as a huge magnet and as such attracts the poles of the magnet. The Chinese navigators utilized this property of the natural magnet around the year 1300 A.D. to find the directions in the sea. This is how the first ‘compass’ of the world was made. In the primitive compasses a cork or a piece of wood used to be floated in a water bowl and a piece of the magnetic stone was placed on it. 

          The modern compasses consist of a small non-metallic box with a thick paper dial covered with a glass plate. The paper is divided into four right angles, each angle representing one direction. They are denoted by N,S,E and W for North, South, East and West. Each quarter of the circle is further divided into eight equal parts. In this way the whole circle is divided into 32 parts. In the centre of this circle a magnetic needle is pivoted which freely rotates in horizontal direction. The magnet pointing in the north-south direction helps the navigators to determine the direction in which the ship is sailing.

          In many ships nowadays, another kind of instrument named ‘gyrocompass’ is also used. In fact, ‘gyrocompass’ is a continuously-driven instrument which acts as a compass. It is unaffected by magnetic variations and is used for steering ships as well.

 

 

          Our earth is surrounded by a blanket of air, which is called the atmosphere. It is mainly composed of nitrogen, oxygen, carbon dioxide, dust particles, water vapours and other gases. The light that comes to us from the sun has to travel through this atmosphere.

           Sun is the main source of light for earth. When the sunlight passes through the atmosphere, it is scattered by the dust particles, water and air molecules in all the directions. This is why, there is light all around after the sunrise.

          We know that the sunlight is composed of seven colours: violet, indigo, blue, green, yellow, orange and red. When the sunrays pass though the atmospheric molecules, the violet, indigo and blue colours get reflected most and the red colour least of them. Therefore, when we look at the sky the light that enters our eyes mainly consists of violet, indigo and blue colours. The mixture of these three colours is almost blue. That is why the sky appears blue.

          If the earth had no atmosphere, the sky would have just appeared dark. This fact becomes very clear when we look at the sky from the surface of the moon. It appears dark since there is no atmosphere in the moon. Similarly, the sky appears dark when we look from a spacecraft, because there are no light scattering particles in the higher space.

 

          In 1820, Hans Christian Oersted of the University of Copenhagen observed that a compass gets disturbed when placed near an electricity carrying wire, and it returns to the normal position when the current is switched off. It made Oersted to realize the magnetic effects of an electric current. Subsequently the relationship between magnetism and electricity was established. The study of this area came to be known as electromagnetism.

          The effects of electromagnetism were first studied by Oersted. Later, Michael Faraday carried out an intensive work on it. The most common explanation about electro-magnetism is that a current flowing in a wire produces a magnetic field. This can be harnessed to produce motion in electric motors through the attractive and repulsive forces of magnetic fields. But Faraday went a step further to question that if a current can create a magnetic field then can a magnet create current? He found out that it is not a magnetic field that creates the current in a wire but the movement of magnetic lines of force across the wire creates the current. When a magnet, either an electromagnet or a permanent magnet, is moved near an electric conductor, turbulent currents are induced in the conductor which move round and round. The conductor experiences a dragging force. This force is used to produce motion and conversely the turbulent currents are regulated to produce an electric current such as in a Dynamo. 

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A nebula is a large cloud of gases and dust in outer space. There are two types of nebulae - diffuse nebulae and planetary nebulae. Diffuse nebulae are much larger than planetary nebulae. Some times a diffuse nebula is close enough to a star so that its dust reflects the light. A planetary nebula is an expanding cloud of glowing gas that surrounds a star.

If we look at the sky at night through a telescope, we can see many big black and white spots. These spots are called nebulae. The word ‘nebula’ comes from Latin which means ‘mist’ or cloud as they give the appearance of mist to us.

Black spots are called ‘black nebulae’, whereas white ones are called ‘bright nebulae’. In reality these nebulae consist of dust, gas and a cluster of stars. Many nebulae are situated in our Milky Way, but many more are outside it. Lot of information has been obtained about them with the help of powerful telescopes.

There are some 2000 nebulae in our Milky Way. It is estimated that there are millions of them existing outside it. Some of them are elliptical, some others are spiral shaped and some do not have any regular shape at all.

The temperature of the nebulae has been found to be varying from 6,000°C to 12,000°C. The temperature of the black nebulae is much less than that of the bright ones. Therefore, they appear black. They contain mostly hydrogen and helium gases. The nearest nebula is 300 light years away from us. And those situated outside the Milky Way are at least 150,000 light years away from us.

Scientists have photographed some of the nebulae. The photograph of the Crab nebula indicates that it is some 6000 light years away from earth. The photograph of one nebula resembles the head of a horse. It is, therefore, named the ‘Horse’ nebula. Another appears like a ring and thus it is called ‘Ring’ nebula. Nebulae are classified depending on whether they emit, reflect or absorb light. Scientists have already studied many nebulae. 

               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.

 

          A microscope is an optical instrument that is used for viewing very minute objects which can not be seen distinctly by the naked eye. Simple microscope or magnifying glass comprising of a single converging lens was known in ancient times. But the first compound microscope is thought to have been invented by a Dutch spectacle-maker, Zacharias Janssen, around 1590. Compound microscopes incorporating “achromatic” lenses became available around 1840s.

          In simple words it is an instrument for producing enlarged images of smaller objects. In modern times we can see magnified images of bacteria, cells of living beings and many other minute objects with it and study their structures. Do you know how enlarged images of minute objects are produced by a microscope?

          A microscope consists of two convex lenses of short focal length fitted at the two ends of a hollow pipe. The lens towards the object is called the objective lens and has a very small focal length. The other lens positioned towards the eye is called the eye lens or eye-piece and has a larger focal length. The object under observation is placed on the platform of the microscope near the objective lens which makes an enlarged real image. This very image acts as an object for the eye lens which makes an enlarged virtual image. Again this image acts as an object for the eye and its image is formed on the retina of the eye. In this way small objects look bigger and their minute structures become clearer. Microscope can magnify the image of an object even up to 1000 times its actual size. Since these instruments use light for illuminating the object, they are called optical microscopes.

          In Electron Microscope, beams of electron are used rather than light to study objects too small for conventional microscopes. It is also used for structural defects and composition studies in a wide range of biological and inorganic materials.

          The various lenses of the electron microscope allow the operator to see details of an object magnified almost upto a million times. However, many specimens may deteriorate under the electron beams at these limits.

 

          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.

          During the rainy season we often see lightning in the sky followed by thunder. Do you know what this lightning is and how thunder follows it?

          In ancient times whenever man saw lightning in the sky and heard thunder he used to believe that gods were angry and punishing him for some sin. Benjamin Franklin was the first person who, in 1872, scientifically explained the occurrence of lightning. In fact, whenever the sky gets overcast with clouds, the small particles of water present in them get charged due to air friction. In the process, some clouds become positively-charged, while some others negatively. When a positively-charged cloud approaches a negatively-charged one, there develops a potential difference of millions of volts between them. Because of this high voltage, there is a sudden electric discharge through the air between the two clouds and a streak of light is seen. This is called ‘lightning’. The electric discharge through the air produces a large amount of heat due to which the atmospheric air suddenly expands. With this sudden expansion, the innumerable molecules of the air collide with one another and produce sound. This is called ‘thunder’. In other words, the thunder is the acoustic shock waves, which may be a sudden clap depending upon the lightning path. Although lightning and thunder are produced simultaneously, yet we see the flash of lightning first. It is so because the speed of light is very high i.e., 300,000 kms per second. On the other hand speed of sound is only 332 metres per second. Thus, because of high velocity, light immediately reaches our eyes, but the sound takes some time to reach our ears.

          Whenever a charged cloud passes by some tall tree or high building, by induction, it produces the opposite charge on that tree or building. When the amount of charge so produced is very high, a giant electric spark travels between the cloud and the ground. It is then said that lightning has struck such a tree or building.

          To protect high buildings from such mishaps, pointed rods of copper or some other metal are fixed on the top of buildings which run to the bottom and are buried deep in the earth. These are called ‘lightning conductors’. Whenever some charged cloud passes by such a building and produces opposite charge on it, the charge goes to earth through the metal rod and does not damage the building. This how buildings are protected from the lightning.

 

          The stars become visible in the sky as soon as there is darkness after the sunset. As the darkness increases, the number as well as brightness of the stars also increase. The number of visible stars dwindles with the approach of dawn. Only very bright stars remain visible. At sunrise all the stars disappear. Do you know why stars are not visible during the day?

          Some people think that as the sun disappears during the night, the stars too vanish during the day. But this is not correct. The stars never disappear. They simply become invisible during the day because of the brightness of the sun’s rays. In fact, the dust, gas and water vapours present in the atmosphere scatter the sun’s rays in all the directions. Due to this, the whole atmosphere starts shining. The light of stars is very weak as compared to the sunlight and as such it fails to make any impact on our eyes. We, therefore, can not see the stars during the day. This fact becomes clear by just observing a burning lamp. During night a lamp’s flame is visible from a long distance, but during the day the same is not visible to us even from a short distance. This implies that even a feeble light can reach our eyes during the night and as such stars become visible to us at night. Had there been no atmosphere, the stars would have been visible even during the day. Stars are visible in the space even during the day because in space you are beyond the atmosphere. 

               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. 

                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.