My Science School

               Mixer and grinder are very useful domestic appliances. With the help of these appliances we can grate, grind and prepare mango shake, milk shake, cold coffee etc. in a short period of time. Butter can be extracted from cream by using this apparatus. Pulses and spices can also be ground easily with its help.

               This apparatus consists mainly of two parts. One is the base of the apparatus which is fitted with a high speed motor. This motor makes 15-20 thousand revolutions per minute. It also consists of a variable switch by which the speed of the motor can be adjusted with the other part of the apparatus known as a mixer and grinder. This is usually made of stainless steel or plastic in the shape of a jar. It is fitted with blades which revolve with the speed of the motor. This rotating blade minces the food material into small pieces.

               Modern mixer and grinders also consist of other attachments such as a juicer with the help of which we can extract the juices of apples, oranges, tomatoes and other fruits and vegetables. In this attachment juice pours out on one side and pulp from the other side. Most modern grinders and mixers can be fitted with various other attachments such as a slice grater, meat mincer, dough maker etc. Nowadays we have grinders by which even wheat or maize can be ground.

               These electrically operated machines have minimized the tedious work in a kitchen. Not only do these machines save time but also provide neat, clean and tasty food for us. Moreover, these machines do not consume much electricity.

                Ammonia gas is a colourless non-poisonous gas that has pungent smell and strong irritating effect on the eyes, nose, throat and lungs. It is highly soluble in water and a compound of nitrogen and hydrogen. One atom of nitrogen on combining with three atoms of hydrogen forms one molecule of ammonia. This gas can be liquefied by compressing or by cooling at -33°C. At normal temperature and pressure, 700 volumes of ammonia can dissolve in one volume of water. Its solution in water is basic in nature and is known as Ammonium Hydroxide.

               There are several methods of making ammonia gas. In the laboratory, this gas is prepared by heating a mixture of ammonium chloride and lime. On a large scale, this gas is manufactured by causing a chemical reaction between hydrogen and nitrogen. This method is called Haber’s Process. In this process one part of nitrogen and three parts of hydrogen are mixed and compressed to 500°C in the presence of iron which acts as a catalyst. Ammonia can also be obtained by distilling coal into coke and coal gas.

                Ammonia is very useful to us. It is used in the manufacture of many of its compounds and also for making nitric acid which is used to dissolve many dry cells. This is also used in the dyeing and printing industry.

                Ammonium sulphate is an important compound of ammonia. It is made from ammonia and sulphuric acid. It is used as a fertilizer because it provides nitrogen for the soil. Ammonium nitrate is used in fertilizers, explosives and for making nitrous oxide, also called, ‘Laughing Gas’.

               The ammonia used as a household cleaner is a strong solution of gas in water. It is also used as cooling agents in refrigerators.

 

               In a football match it is our common experience to see that when a player kicks a resting ball it moves in a certain direction. Similarly when the goal keeper grabs the ball firmly with his hands it stops moving and remains at rest till it is released again. Do you know why it happens so? In both these actions force is applied on the ball.

               Force is a physical quantity which, when applied to a body tries to displace or displaces it. This quantity is equal to the product of the mass of the body and its acceleration. The unit for measuring force is Newton or Dyne. Force is required to set any body in motion and this force is applied in a particular direction. The force is an external agency capable of changing the rest or motion in an object or a body. When force is applied on a body and it gets displaced, we say that work has been done on the body by force. The amount of work done by the force is equal to the product of the force and the distance covered by it. A work done by force is measured in Joules. In short, force is a vector quantity possessing both magnitude and direction. 

 

 

 

           

   The capacity of doing work is called energy. Everything in the universe has some energy by which it can do some work. We experience energy in many forms such as mechanical energy, heat energy, light energy, electrical energy, magnetic energy, chemical energy, nuclear energy etc. 

 

 

 

 

 

 

             Mechanical energy is of two types: potential and kinetic. Potential energy is due to the position of the body while kinetic energy is due to the motion. One form of energy can be converted into the other form of energy. Winding a watch spring stores potential energy. This stored energy gets converted into kinetic energy when the watch starts running. Although energy can be converted from one form to the other, yet the total quantity remains the same. 

 

 

 

 

 

               Some people confuse between power and energy and think of both as the same. But it is not so. Total energy of a body is equal to the capacity of the work done by the body while power is the rate of doing work by the body. It is equal to the amount of work done in unit time. The system to measure unit of power is called horse power (hp) or watt. Horse power is the British unit of power. 

 

 

 

 

 

 

               One horse power is equal to 735.7 watts. The word ‘watt’ is derived from the International Systems of Unit and named after the British engineer James Watt. 

               Embossing is the process of producing raised patterns on a surface. This is one of the oldest methods to decorate metals. A technique widely used for making ornaments is in which a thin metal sheet is decorated by beating it on the underside. This type of embossing is usually done either by hand or with a die and a counter die. It is usually called repouses. The materials suitable for embossing are plastics, thin metals, papers and leathers etc.

               Crests, monograms, and addresses may be embossed on paper envelopes from dies set either in a small hand-screw press or in an ordinary letter press.

               For impressing embossed pattern on wallpapers, textiles, copper cylinders are engraved with the desired patterns to be raised.

               In this process the pattern is drawn or inscribed on the face of the die called male die. The surface is then machined away around the pattern so as to leave it raised. The counter-die termed as female die is engraved to match this die, so that when a thin strip of metal is placed between them and the die is forced into the counter-die, the pattern is left impressed or embossed upon this thin strip of metal. Die stamping has been used for many years for manufacturing metal parts. This method is also used in stationaries and letterheads. In this method paper is pressed between the dies and ink is applied to the top surface at the same time. Printers nowadays are using embossing machines for this purpose which produce raised patterns in a very short period of time. Blocked ornamental design on book covers or imitation tooling on letter work for instance, can be beautifully affected by means of powerful embossing presses.

               Small hand-operated embossing machines have become very popular. The letters and numbers are embossed on a strip of soft metal or more commonly used vinyl tape. These are then formed by the hand-operated embossing machine. A wheel is used for pressing which transfers the pattern onto the other strip.

               Modern embossing machines are equipped with latest electronic devices. They are replacing the hand-driven machines gradually. But still, a few traditional users of embossed material, such as ornaments prefer the old technique in making their ornamental designs.

 

               A hydrofoil is an underwater fin which consists of a flat or curved plane surface and is designed to lift a moving water vehicle by the reaction on its surface from the water through which it moves. Hydrofoils are used with ships and motor boats.

               The first hydrofoil was invented by an Italian called Forlanini in 1898. In 1918 a hydrofoil powered by an aircraft engine, gained the world’s water speed record. Hydrofoils were not widely used until the 1950s. After 1950 their use became common in military and commercial ships. By the 1970s hydrofoil craft were in operation in many places and speeds of upto 80 knots were achieved. During 1950s hydrofoils were developed in the United States, Canada and Russia.

               Now the question arises, how does a hydrofoil work?

               We know that water is 775 times heavier than air. And so very small hydrofoil wings can support relatively heavy boats. But since water puts great loads on boats, the hulls are usually built of high strength steel.

               The function of the hydrofoil is to raise the hull from the water so that the resistance caused by friction is reduced. This means the power needed to drive the boat at high speeds is reduced considerably. Another advantage of hydrofoil is that it can travel smoothly even in rough water.

               Hydrofoils are of such a shape that the flow of water over them causes a lift. As the boat’s speed increases it raises out of the water, supported on wing-like struts or foils. The hull lifts farther and farther out of the water until it is clear. Under this condition the only parts then in contact with the water are the hydrofoils and supporting struts and the propeller shaft.

               Hydrofoils are of various designs. While some boats have V-shaped or surface piercing hydrofoils, others have variable angle foils that can be adjusted. The purpose of all these is to lift the boat above water surface so that water friction does not produce any resistance. Hydrofoil boats can travel at a high speed. Nowadays hydrofoils are being used on a large scale in naval ships and commercial boats.

               The largest hydrofoil was launched by the Lockheed ship-building and Constructions Company, Washington, on 28 June, 1965. The 64.6 metre long hydrofoil has a service speed of 92 km per hour.

               A television is an electronic device which produces audio and visual effect simultaneously. It is not only a means of entertainment but also a great source of education. The basic theory of television was developed by the English scientists, Ayrton and Perry in 1806. The idea developed by them was called Electric vision.

               Televisions are of two types: black and white, and colour. Colour television functions quite like a black and white television set but its working is much more complex.

               The colour television has mirrors inside the camera which divide the light into three parts. There are three filters inside the camera, one for each part of the light. One filter allows only red light to pass, another allows only green and the third only blue. Each colour goes to a different camera tube and each tube has a separate glass plate and electron beam. From the three tubes three signals go to the transmitter.

               The colour television transmitter multiplexes three signals into one. To this resultant signal a black and white signal is added. This combined signal is sent to the broadcasting antenna. From here this signal reaches our television.

               In colour sets three electron beams - red, green and blue, scan the screen which when mixed together give full colour picture. The screen of the picture tube is coated with  million tiny dots of phospher, each arranged into a group of three. A phospher is a substance that emits light when an electron beam falls on it. Each of the three phosphers emits three colours - red, blue and green. So the blue phospher emits blue light when the electron beam carrying the blue light signal falls on it, and so on. The colour produced at each group of dots depends on the intensity of the electron beams. To make sure that each beam produces the right colour, the beams pass through holes in a shadow mask behind the screen. These three colours can be produced in different proportions to give all the other colours of the original.

               In a modern television set, all its functions can be regulated by remote control system which includes sound adjustments, colour perfection, channel changing and so on. 

               Sodium lamp is used for street lighting. It is also used in research laboratories as a monochromatic source of light, as it produces bright yellow light which is quite pleasant to the eyes. Do you know how does this lamp work?

               A sodium lamp is operated on alternating current. It consists of a U-shaped glass tube with two electrodes of tungsten spiral coated with barium oxide. The tube is evacuated and neon gas at low pressure of about 10 mm of mercury is filled along with a small quantity of metallic sodium or sodium vapour. This discharge tube is enclosed in an unsilvered vacuum jacket to avoid heat loss. For electric discharge a voltage of 400 volts is applied to the electrodes with the help of a transformer. Initially neon gas gets discharged and red light is produced, due to this sodium atoms get excited and produce yellow light. Because the ionization potential of sodium is higher than neon gas, the lamp produces more of sodium light.

               The working temperature of the lamp is about 250 degree centigrade. If this temperature is not maintained constantly the intensity of emitted light would be considerably varied. The sodium light contains only two wavelengths, viz 5890°A and 5896°A. Sodium lamp is also used for outdoor illumination as the characteristic yellow light is less absorbed by fog and mist than white lamp.

 

               Acoustics is the science of the production, transmission and effect of sound. Cinema halls, lecture halls and auditoriums are designed in such a way that speeches or music programmes can be heard clearly by the audience. While designing such buildings it is always taken into account that no echo is produced. Do you know how the buildings with good acoustical quality are designed? Architectural acoustics is now an integral part of modern architecture.

               While designing such buildings it is kept in mind that the sound of the speaker is neither too loud nor too low so that it is clearly audible to everyone in the hall. Normally some materials such as plaster reflect the sound. Other materials, such as carpets, clothing, draperies and human bodies absorb sound. Thus in an auditorium a perfect balance has to be maintained by placing these things in such a way that the reflection and absorption of the sound is evenly spread.

               Two properties of sound help the builders a great deal in designing the buildings of good acoustical qualities. These properties are echo and reverberation. An echo is a sound that has been reflected from a surface. Substances which reflect sound produce strong echoes. In an auditorium, we hear the sound from two sources: directly from the speaker, and from a surface. It has travelled farther than the direct sound. This means that it reaches our ears after the direct sound. In a properly designed room, the echo and direct sound are heard almost at the same time, thus ensuring that there’s no disturbance and the sound heard is clear and distinct. But in a poorly designed room, the time gap between the two is quite long and as a result sound is not heard clearly.

               A reverberation is defined as a close group of echoes i.e. echoes and re-echoes. Each successive echo is quieter than the previous one. One can minimize echoes and reverberations by building rooms with sound absorbent materials. But then the sound in such a room would have a dead quality. A certain amount of reverberation is also required for good quality of sound. In general, the reverberations should last for 1 to 2.5 seconds. This is called the reverberation time.

               Another difficulty encountered while designing an auditorium is the volume of sound. People sitting at the back of the auditorium should be able to hear as clearly as those in front. For this purpose sometimes sound has to be amplified by loudspeakers. Often this is not a very satisfactory arrangement as loudspeakers do not reproduce sound very accurately.

               In designing good sound quality rooms, we must consider pitch or frequency also. Sounds with different pitches can be reflected from surfaces in different degrees. Resonance also must be avoided. Due to resonance one particular frequency sounds much louder than the others. The frequency of sound waves makes sound high or low. If the high frequencies are loud, we hear shrill sounds, and if the low frequencies are too loud, we hear dull sounds.

               Ancient Greeks were the first people to build their theatres with good sound qualities. They placed their audience on steep hillsides where sound could travel to them directly. These theatres were called amphitheatres. The speaker’s stage was parallel to the first row of seats at the bottom. And thus every member of the audience could see and hear well. The Hollywood Bowl in California is a modern-day amphitheatre. Modern hi-fidelity equipments can reproduce sound with life-like clarity.

 

Cathode rays are streams of electrons emitted from the negatively charged electrode or cathode when an electric discharge takes place in a vaccum tube. They are called cathode rays as they are emitted from the cathode.

To produce the cathode rays, a glass tube fitted with two electrodes at its open end, is used. Electrodes are connected to a D.C. source of high voltage. The electrode which is connected to the positive terminal of the electric source is called anode, and the one connected to the negative terminal is called cathode. The glass tube is connected to a vacuum pump. When the pressure inside the tube falls to about  mm of mercury and the high voltage supply to the electrodes is switched on, a particular type of rays emanate from the cathode. These are the cathode rays which produce fluorescent effect in the tube. These rays move towards anode. Experiments have proved that the properties of these rays do not depend upon the gas present in the tube. The charge on the electrons and their mass remain the same. These rays have some specific properties as follows:

1. These rays travel in straight lines.


2. Their direction is always perpendicular to the surface of the cathode.


3. They possess mechanical energy so exert pressure.


4. When these rays fall on certain substances, they produce a fluorescent effect.


5. When these rays hit some substance, the temperature of the material rises.


6. They can penetrate through thin metallic foils.


7. They can ionize the gases on which they fall.


8. The velocity of these rays lies between  to  of that of the velocity of light.


9. These rays get deflected by the magnetic field.


10. They are also affected by electric fields.

Cathode rays are very useful to us. When they fall on a metal like platinum or tungsten they produce X-rays. X-rays are very useful in science, industry and medical sciences. Cathode ray tube is also used as an indicator in radar systems in which electric signals can be seen on a fluorescent screen.

 

               Bernoulli’s effect is an important derivation in mechanics and fluid dynamics. It was first described by the Swiss mathematician Daniel Bernoulli. This is also known as Bernoulli’s principle. He published this theory in 1738 applying mathematical calculus to that science.

               According to Bernoulli’s effect in any small volume of space through which a fluid is flowing steadily, the total energy comprising the pressure, gravitational potential and kinetic energy is always constant. In fact, this theory propounds the law of conservation of energy for flowing fluids. It also states, if the velocity of a horizontally flowing liquid or gas increases, its pressure decreases. This effect has many applications in mechanics.

               Bernoulli’s effect has helped a great deal in the development of aerodynamics and applied in the design of Airfoil. An aeroplane wing, seen from the tip, is flat at the bottom and curved at the top. As the wing travels through the air, the air must travel either over or under the wing. Air moving over the wing goes a longer distance so it must travel faster. Because the air moving over the wing is travelling faster, there is less air pressure on the top of the wing. This means that there is more pressure on the bottom of the wing, which pushes the wing upward, causing the aeroplane to stay up in the air. 

Continue reading "What is Bernoulli’s Effect? "

               A water or lift pump, often called a tube well, is used to lift water from a lower level to a higher level. These pumps are used in houses or on roads for boosting up the underground water. They work on the principle that atmospheric pressure can support a vertical column of water upto 9 metres in height.

               In this pump, an iron pipe is put into the ground up to the level of water. On the top of this pipe, another pipe of bigger diameter is fitted. Several components of the pump are fitted into this pipe. It consists of a handle which is connected to a piston which moves up and down, inside the barrel. It contains two valves, of which one is fitted with the piston and the other at the junction of the two pipes. Both these valves open only in the upward direction.

               When the piston is pulled up with the help of the handle, the pressure in the iron pipe falls. This opens the valve fitted at the junction of the two pipes closing the upper valve. During this action, the pressure above the surface of water becomes less than the atmospheric pressure. This makes the water rise up in the pipe.

               Similarly when the handle is pulled up, the piston goes down and the valve at the joint closes due to the weight of water. Now the compression of water opens the upper valve. This makes the water rise up further. With this repeated action the water level continues to rise until water comes out at the top.

               However, this pump has two limitations. Firstly, water is discharged only on the upward stroke. And, secondly, although in principle, it can lift water upto a height of 9 metres, in practice it is only about 8 metres (or 30 ft) above the water surface.

               The modified version of this pump is called force pump. In this pump, the upper valve is not fitted to the piston but to the opening. With this modification, the water can be pumped to a much higher height. Force pump can raise water from greater depths and is used to send water to the upper floors of multi-storeyed buildings. For the continuous supply, centrifugal pumps are used these days. These usually run on petrol, diesel or electricity.

 

            Lathe is a widely used machine in the workshops. It is primarily used to give a round shape to materials such as wood, metal or plastic. It is also used for cutting screw threads. Do you know how a lathe machine works?

            A modern lathe consists of an electric motor which spins the given material on a horizontal axis. The speed of the motor can be regulated according to the requirements. This motor rotates a chuck. The work piece is mounted on the chuck. When the motor revolves, the chuck also revolves with it. A cutting tool is brought against the spinning material which cuts away the material until the desired shape is formed. The cutting tool is mounted in a special holder and can be moved in several directions — up and down, and from one side to another.

            Lathes also have a sliding tailstock which is used for centering the work piece. By mounting a drill bit with the tailstock it can be used to drill holes into the work piece.

            Lathes are extremely accurate. They can perform shaping and cutting operations, upto an accuracy of .0002 cm. The most widely used type is the centre lathe or engine lathe. Another popular type of lathe is the turret lathe. In the tool holder of this lathe, six cutting tools can be mounted. This makes it possible to bring several different kinds of cutting tools into use without stopping the machine. Moreover, once the cutting tools have been set, the same operations can be done on piece after piece. When thousands of such operations are needed, a multiple spindle bar machine is used. It is a kind of lathe that performs six different operations. A single computer can run many lathes in large automated factories. A person mounts the work pieces in the lathes and removes them when work is over. Until 1800, lathes were crude machines which could perform a few basic operations only. Around 1800, Henry Maud slay of England, invented the first thread cutting machine. In 1873, C.M. Spencer of USA developed the first fully automatic lathe. By the end of 1900s, a form of automation called numerical control was used to run many lathes at the same time.

 

            We know that electricity is generated at power stations through large generators. Normally power stations are of two types: hydraulic and thermal. These power stations are at a distance from cities to avoid pollution. Electricity is transmitted to the cities and villages with the help of the transmission lines. Do you know how it is done?

            Electricity is transmitted with the help of two parallel wires. In modern power stations the voltage increases as much as 400,000 volts. The reason is that the power lines which carry the electricity lose power if it travels of low voltage and therefore, the voltage is increased in a step-up transformer. The current is then fed into a network of high-voltage power lines called “Grid”, which distribute electricity for use through different sub-stations and underground cables or overhead wires. But before it can be used, the voltage is lowered suitably in a stepped down transformer.

            Big factories and industries may consume current of several thousand volts, but for domestic use of current, it may be upto 220 volts. In this way electricity is transmitted from power stations to distant areas.

 

               Two centuries ago there were two conflicting theories of light. These were Corpuscles Theory suggested by Isac Newton (1642-1727) and Wavelength Theory propagated by Christian Huygens (1629-1695). The theory of Huygens was subsequently established by an English physicist Thomas Young (1773-1829). Newton suggested that a beam of light consists of tiny particles (corpuscles). And since light was corpuscles, Newton argued, it travels in straight lines and casts sharp shadows. It also explained as to why mirror-reflected light simply bounced off the glass like tennis balls off a wall. Newton thought it might be caused by the corpuscles that travel faster in glass and water than through air.

               In contrast, Huygens believed that light travelled in waves like ripples on a pond. He also showed that each colour of light has a different wavelength. He proved that light travels slower through glass and water than through air. The amount of refraction, that is, the amount of light is bent depends upon the light. The shorter the wavelength the more is the bending. 

               In 1801, Thomas Young, based on the theory of Huygens, established the wavelength theory beyond doubt. He shone a beam of light through silts in a piece of card. The silts divided the light into two beams which when recombined, formed a pattern of alternate light and dark bands on a screen. He reasoned that the pattern was produced by interference between the waves of two beams.

               Now, what is actually interference of light and how it is defined? According to Huygen’s theory, light waves spread out from their source in ever increasing circles. It tells us that where two light waves meet, they combine in some places on their way and cancel out each other. This process is called “interference of light”. When two wave-lengths of light met they reinforced each other and produced a bright band. On the other hand, where one crest (higher part of the wavelength of light) met another they cancel each other to form a dark shade.

               It is interesting to note that for more than a century, Newton’s theory seemed more popular because of his name and fame. This position was changed when Thomas Young convincingly proved and established the wavelength theory of light. His experiment on “interference” was important among other experiments conducted by him in this connection.

               Today, modern physicists explain the optical phenomena of light in terms of waves, e.g. interference, refraction, reflection, or diffraction.  

               A battery is a device that produces electricity by chemical action. It contains more than one cell. Each cell produces its own current. Batteries with several cells are used to provide electricity for automobiles, heavy equipments, space crafts, submarines and emergency electric lights.

               The battery which is used in a car is called a storage or wet battery. Storage or wet battery like car battery has a greater capacity and produce more electricity in comparison to other batteries. It can be recharged again and again in order to use for a considerably longer period. The first such battery was invented in 1859 by a French physicist, Gaston Plante.

               Storage or accumulator batteries are of two types: acid accumulators and alkali accumulators. Lead-acid batteries consist of plastic or hard-rubber containers. These batteries are used in cars throughout the world. Each cell of this battery contains two sets of electrodes. The pairs are suspended in dilute sulphuric acid. One electrode is positive and the other negative. One electrode is made of spongy lead and the other of lead dioxide. The separator plates keep them apart. This cell requires distilled water. Such a cell has a potential difference of 2 volts and the cells are connected in series. Most car batteries have 6 cells, giving 12 volts in all.

               At the positive electrode, lead dioxide reacts with hydrogen and sulphate ions of sulphuric acid and forms lead sulphate and water. In this reaction, two electrons are obtained from the wires which balance the chemical reaction. At the negative electrode, lead reacts with sulphate ions and forms lead sulphate. This provides two electrons to the wire which maintains electrical balance. The net effect of this reaction is that electrons start flowing from the negative plate to the positive plate.

               When the lead of lead dioxide is over, the cell stops working. This cell can be re-charged by making the electricity flow from the negative to the positive plate.