My Science School

Electric heaters, immersion heaters, electric irons, electric kettles, etc. are appliances which produce heat through electricity. All these appliances are based on the heating effects of electric current. When electric current is passed through a wire, it gets heated up. Heating of a wire depends upon two facts: first, on the resistance of the wire and then on the amount of electric current passed. The heat produced in the wire is directly proportional to the resistance of the wire and that of the square of the current. The amount of heat produced also depends upon the time for which the current passes through the wire.

Based upon this property of current, many domestic electric appliances have been developed. The working principle of all these appliances is almost the same, the difference lies only in their construction. An electric heater consists of a coil of nichrome wire which is in the form of a spring. This coil is mounted on an insulating base plate made of clay. When electric current is passed through the coil, it gets heated up. Room heaters are also made in a similar way, the only difference being that nichrome wire is wound around an insulating rod and a reflector is mounted at the back of the coil which reflects the heat radiation.

Immersion heaters also consist of a nichrome wire which is enclosed in a metal tube. To isolate the wire from the metal tube, an insulating powder is filled in the tube. This powder acts as an insulator for electricity but conducts heat. When the two terminals of the wire are connected to an electric source, the current starts flowing through the wire and it gets heated up. The immersion heater is put inside a bucket full of water to heat the water.

An electric iron is used to remove the wrinkles from washed clothes. This appliance also consists of a ribbon of nichrome wire which is enclosed between two sheets of mica. This spreads the heat uniformally along the base plate of an electric iron. Mica sheets are mounted on a heavy metal plate. This metal plate, when pressed against the surface of the cloth, removes the wrinkles from the cloth.

Electric irons are of two types: automatic and manual. Automatic one is fitted with a thermostat control which regulates the temperature. Manual irons do not have such a device. When the iron is cold, thermostat provides and maintains a constant temperature by the use of a device that cuts off the supply of heat when the required temperature is exceeded.

An electric kettle is used to prepare tea or coffee. It also consists of a heating element fitted at the bottom of the vessel and is isolated from it. Water is put into the vessel which gets heated when current is passed through the heating element.

For all electrically heated appliances, it is very essential to have an earth connection. Immersion heaters should not be switched on, until there is water in the bucket. The electric bulb is also a similar device whose filament gets heated up when the electric current is passed through it and it produces light.

 

               Electric fans have become an essential part of our lives. It provides a cooling effect during the summer and rainy seasons. Do you know how does it work?

               An electric fan is a device which converts electrical energy into mechanical energy. It works on the basis of magnetic effects of electrical currents.

               The heart of an electric fan is an electric motor. So before understanding the working of a fan, it is essential to know the working principle of an electric motor.

               In its simplest form, it consists of a coil or armature through which the current flows. It is connected with a spindle. This coil is placed in between the poles of a magnet. When the electric current flows through the coil, it starts rotating due to the magnetic effects of electric current. This motor consists of a split-ring commutator to which two carbon brushes are attached. The armature of the motor is connected to a metal shaft. At the other end of the shaft, three or four blades made of a light metal are attached which also start rotating along with the motor. These blades are designed in such a way that when they rotate, they suck in air from one side and throw it to the other side, thus causing strong air currents. 

               The speed of rotation of the motor can be controlled by controlling the current which is done with the help of a regulator. This regulator consists of a resistance which controls the amount of electricity flowing through the coil.

               Usually electric fans are of two types: ceiling fans and table fans. The domestic electric fans are usually rated from 60 watts to 120 watts.

               A third type is often used in underground establishments, kitchens, cinema halls, stores etc. to expel the polluted air. These are called exhaust fans. The blades of these fans are so designed that they suck in the air from inside and throw it outside. These are also used in air coolers.

               Now the question arises as to how the air of the fan gives us the cooling effect? The fan increases the speed of air currents and this brings about an increase in the rate of evaporation. Since evaporation causes cooling, a running fan produces a cooling sensation.

 

               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.

               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.

 

               We all have seen the digital watches and calculators. These devices make use of liquid crystals for displaying various digits. Liquid crystals belong to a state of matter having the mixed properties of both the liquid and the solid states. Liquid crystals may be described as condensed fluid states with spontaneous anisotropy.

               Liquid crystals are of two types: thermotropic liquid crystals prepared by heating the substance and lyotropic liquid crystals made by mixing two or more compounds. Some of the important liquid crystals that belong to the first category are p-azoxyanisole, cholesteryl nonanoate and p-n octyloxybenzoic acid. In the second category sodium stearate and alpha-lecithin are the two important liquid crystals. Liquid crystals are used in colour T.V. and electronic display tubes, sensitive tapes and electronic devices for digital clocks, watches and calculators.

               Light emitting diodes are also used for this purpose but liquid crystals need lesser electric power and have great clarity even in the presence of bright light. 

               Liquid crystal displays work on two principles, viz dynamic scattering and field effects. In displays the liquid crystals are sandwiched between two transparent electrodes (glass coated with a metal or metal oxide film). The thickness of a liquid crystal film varies from 6 to 25 microns. The cell is sealed to eliminate oxygen and moisture.

               In dynamic scattering, if no electric field is applied, the cell is transparent. On applying electric field to the crystal the cell becomes opaque. Digital displays are made by photo etching a seven-segment pattern on tin or indium-coated glass plate.

               The field-effect displays are mostly used in watches and calculators. The output of quartz crystal is given to seven segments of liquid crystal in a watch. Polarizers are also used for liquid crystal cells. Electric field changes the molecular alignment by which liquid crystal becomes opaque on account of a mirror behind the second polarizer.

               Liquid crystal displays have revolutionized a number of fields. Nowadays thermometers with digital displays are also available in the market. 

            When someone wants to take a photograph in dim light or darkness, he makes use of a flash-gun with his camera. As soon as the shutter of the camera is pressed, flash gun produces its own light and illuminates the object. Do you know how does a camera’s flashlight work?

            A modern flash-gun consists of a light source which is usually a xenon flash lamp. To operate the flash lamp there are electrical circuits and an electric source which gives energy to the flash lamp. Electric source is usually a dry battery.

            A xenon flash lamp is a glass tube - usually two inch long with quarter inch diameter. Two tungsten electrodes are sealed at the ends of this glass tube. This tube is evacuated and filled with xenon gas at a pressure of 400 to 500 mm of mercury. A thin wire is wound around the tube which acts as the third electrode and is known as trigger electrode. The two electrodes of the lamp are connected to the electric circuit which consists of a capacitor bank to store the electrical energy. When shutter is pressed, the electric switch is also pressed and a high voltage pulse comes on the third electrode. This high voltage pulse ionizes the xenon gas by which it becomes electrically conducting. At this point, the energy stored in the capacitor bank gets discharged through the xenon lamp. As a result light is produced which illuminates the object to be photographed? At the back of the xenon lamp, a reflector is mounted which directs the light towards the object.

            Unlike a flash bulb, an electronic flash can be used again and again. The flash contains a tube that gives out a bright flash of white light when a strong electric charge passes through it.

            The light emitted from the flash gun is in the form of a pulse. Its duration is about one millisecond but the light is very intense. Nowadays almost all cameras are fitted with the electronic flash devices. 

               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.

 

               We know that light is a form of energy and it travels in the form of electromagnetic waves. These waves are made up of electrical and magnetic vectors which are perpendicular to each other and also to the direction of propagation. The electro-magnetic theory of light was propounded by a physicist Maxwell. This was a very comprehensive theory, but yet could not explain certain phenomena of physics.

               We know that red hot objects usually emit red light. The frequency of this light does not depend upon the substance which is being heated up but upon the temperature of the substance. Efforts were made to establish a relationship between temperature and frequency on the basis of electromagnetic theory. But, the theory failed to explain the frequencies of ultraviolet light. 

               However, this problem was solved in 1900 by a German physicist, Max Karl Planck. He suggested that light is emitted in bundles or packets instead of a steady stream. And this packet of light was called quantum. The contention put forth by Planck is now known as the Quantum Theory. According to this theory the energy of each quantum is proportional to its frequency.

               In 1905 Quantum Theory solved another problem of photoelectric effect. It enabled the famous German physicist, Albert Einstein to put forward his theory of photoelectric effect. He named the light quantum as photon.

                Later, Quantum Theory was used to explain many mysteries of atom. Today it has become possible to explain many effects of physics on the basis of quantum theory. Now physicists think of light as waves for some purposes and as quanta for other purposes. However, there is a highly respectable version of Quantum Theory developed recently by John Cramer, of University of Washington. His interpretation is simple and provides a new insight into the significance of the present research in this field.

               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.