My Science School

               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.