My Science School

The colour of an object is determined by the spectral composition of the light reflected by it. When a surface is dry, the reflected light rays corresponding to the colour of the surface are superposed with diffused white light arising out of random scattering resulting from the roughness and irregularities of the surface. In the case of clothes, this superposition tends to fade the reflected colour.

 If clothes are immersed in water, all the kinks and interspaces are filled with water. This minimizes scattering of light on the surface. So the reflected light comes out unsuppressed with the basic hue of the cloth. Hence it looks richer and darker than when dry.

 The effect is conspicuous on cotton clothes as the fibres are loosely packed with a lot of microscopic air spaces. This increases the surface area and consequently the scattering of light. Hence cotton clothes look light when dry and dark when wet. The effect is not so much in synthetic and silk clothes as their surfaces are smoother and very little water is absorbed by them. 

 When any TV is switched on, electric power is supplied to both audio and video sections. The video section consists of a cathode ray tube which is commonly called as picture tube. An electron beam is used to sweep the screen to display the pictures. This electrons beam is generated within the CRT using a filament which can emit electrons only when heated. This heating process requires sometime. Audio section does not need any such ‘warm up’ to start functioning and so we hear the sound as soon as we switch on.

 

This technique is often used in real-life crime programmes to protect innocent individuals or to avoid suspects receiving unfair trials.

The process of pixilation works as follows: for each square pixel area, the computer measures the brightness and colour of each point and calculates the average. This average value is then assigned to the entire pixel. Thus the properties of the picture to be obscured, in this case a face, are largely retained. However, each square has sharp edges, and since the edges are a product of the pixilation process and not related to the elements of the face, they obscure the picture. The reason the face still seems to move is because although the position of each square will remain constant, the person “behind” the pixilated area will be moving, and therefore the average values for brightness and colour change. Squinting, screwing up your eyes or, even better, removing your spectacles blurs the image and prevents you from seeing the sharp edges of the squares. You are then left only with a face in which changes in brightness and colour have been smoothed by averaging, and which is then much easier to see and identify.

The same effect can be achieved by making the pixilated face smaller, or by moving it further away - the edges become too fine to observe their detail and disappear and the face is more easily seen. This effect was first described by Leon Harmon in 1973 (Scientific American, vol 229, p 70). 

The artist Salvador Dali made use of a sort of a “pixilation” technique in some of his paintings, one of which is pictured aside. These images were unreadable until one moved a certain distance from the picture or if one did some serious squinting. The pixilated painting below illustrates the point. When you view the picture from close quarters you see a woman walking through an opening. From further away, all you can see is the face of Abraham Lincoln, the former president of the U.S. With computers the effect is far more accessible. Simply take a bitmap image of anything, but preferably something small, and zoom in on it until you can see the pixels. The more you zoom in, the less clear the picture becomes, and the more you need to squint to see it.

  

     The connection between any two subscribers is through a Local Switching Exchange (or) Central Office.

It is a hard wire connection in series with the earphone and carbon microphone of each telephone handset with a battery. The Local Switching Exchange or the Central Office (CO) employs a battery plant.

 

To make a phone call, a subscriber lifts his handset (receiver), so that a switch called “off-hook” switch in his telephone set is “on”, and he gets connection with CO. The CO sends a dial tone signal to his handset. As he dials a number, each digit is identified as interrupted line current at the CO. The CO with the help of a panel full of digital circuitry examines whether the line corresponding to the digits dialed by the calling party is free. The line will be found free only when the off-hook switch at the called party's hand set is off. If the line is free, the CO - immediately places a “ringer generator voltage” (50V 20Hz, “On” 2 seconds, “Off” 4 seconds) on the called party’s line as well as part in the calling parties’ line. This timing is different for outer exchange calls. We hear only this ringer sound, being sent from the CO. The timing is different for outer exchange calls.

When the called party at the other end lifts his handset to answer, the off-hook switch in his handset is “on” and only now, his (handset),receiver gets life and making him capable of hearer speak. So the receiver the other end is enabled only when it is lifted there by making the off-hook switch “on”.

As long as the conversation between two subscribers being established, it is the CO which communicates with the calling party just as sending.

 

 Rice contains starch, a polysaccharide made of amylose and branched amylose amylopectin. In rice, it takes the form of granules which are clustered together to form compound grains. The dried starch granules when soaked in water swell and continue to do so when temperatures are is raised. Above a certain temperature the swelling becomes irreversible and the starch is gelatinized.

Lower the amylose content of starch, greater is its swelling. As rice starch has comparatively low amylose, it swells to a large extent on heating. This boiled rice when crushed becomes a paste which can be used as an adhesive.

  A stainless steel femur rod does not set off airport metal detectors because it is made of non-magnetic stainless steel.

            Stainless steel is made in two forms: austenitic and ferritic. Austenitic stainless steel is nonmagnetic. It is the common form used in cooking pots and for surgical hardware.

            Ferritic stainless steel is magnetic. It is used in some knives and guns and for various industrial purposes.

            Non-stainless steel (carbon steel) is magnetic. It is used in most knives and guns.

            Metal detectors do not detect metals as such; they detect the distortion of a magnetic field produced by materials of high permeability.

            Magnetic materials have high permeabilites which greatly distort the field and so are ready to detect.

            Nonmagnetic materials have low permeabilites and as a result have little effect on the field and are difficult, if not impossible, to detect.

            The small bunch of keys detected at the airport is probably on a magnetic steel ring because most keys are made of nonmagnetic metals, such as brass or aluminum.

            One can avoid setting off airport metal detectors by limiting the number of bank credit cards (they have magnetic stripes) and by touching all the metal things with a strong magnet and not carrying those it attracts.

Generally tyres of vehicles are filled with air to absorb the shocks generated as the vehicle moves on uneven roads, and make the ride comfortable.

The shock absorbing capacity is enabled by a fundamental property of air namely compressibility - air gets easily compressed to smaller volumes on application of pressure.

But water is not compressible and so if one uses it to fill the tyres, all the shocks generated on the tyres will be completely passed on to the vehicle and its passengers will feel the discomfort.

In addition water-filled tyres increase the rolling resistance of vehicles because of the increase in weight. Hence apart of the engine’s power and fuel is wasted in overcoming this resistance.

Tubeless tyres are not popular in India because of two reasons. First, rusting of rims, which leads to air leak, is a perennial problem in the tropical climate. Second, fitment of such tyres needs special tools and presses and so they cannot be repaired in road-side shops. In conventional tubed tyres, load is carried by a volume of air held inside a tube which is closeted to the inside of the rim at the bottom and to a tyre over the remaining area. In tubeless tyres, the type itself holds the air. Outwardly, a tubeless tyre resembles a tube tyre. The inside of a tubeless tyre has an airtight lining extending the beneath the bead (the part of the tyre that anchors it to the rim) when inflated. In order to provide perfect sealing, a special coat of rubber is provided to the inside wall of the tyre which is fitted to the rim using rubber seals. The special bead seating (on the rim) also prevents air leak. There is no need for a flap and so a value is fitted to the rim itself for inflating or deflating the tyre.

 Tubeless tyres have distinct advantages over conventional tubed tyres. For example, down time is reduced due to the elimination of tube and flap troubles, and fitting is easier. It gives cooler running - which is important in high ambient temperatures and on long hauls.

Unnoticed accidental damage can lead to a burst with tubed tyres. (The air escapes through the tube-tyre interspace). Such damage shows up as a slow leak in tubeless tyres. There is no run-flat situation and so the user can safely travel up to 10-15 km before setting it right. These obvious advantages of tubeless tyres have led to its adoption in many other countries. 

Automotive tyre consists of a number of rubberized fabric layers and the layer is called ply. A collection of such plys is called carcass or casing. It is this casing which is responsible for the tyre’s performance including its load bearing capacity.

Originally cotton tyre fabric was used. Irrespective of the nature of the fabric nylon/rayon/polyester), the strength of the carcass is equated to the number of ply. This convention is still followed in cross-ply tyres.

 For example, the 8 ply-rating of nylon fabric reinforcement implies that the strength of the carcass is at least equal to 8 cotton plies. But the actual number of nylon fabric ply could be 4 or 6 (because nylon is much stronger that of cotton). But this numbering system is beset with two misconceptions: One is that the tyre consists of that many of plys and the other one is that the strength of the carcass is limited to the number of plys. 

To overcome this, nowadays, the ply rating is also indicated in alphabetical letters. 

Ply rating of tyres is the number of layers of soft rubber-clad fabric below the tread (rubber layer) of a tyre. The fabric nylon or rayon is subjected to tension before calendaring. The tensioned fabric is then rolled between steel rolls with rubber on top and bottom of the fabric. The calendar is then cut at 45 degrees according to the width of the tyre to be manufactured. The cut calendar is placed on the drum with rims on both sides of the drum to make a skeleton of the tyre. The tread (rubber) is placed on the skeleton and pressure is applied to stick the tread-to the calendar. Later on it is cured and moulded to actual shape. 

       Ordinary tyres or cross-ply tyers are the oldest type of tyre and has a case made of two or more layers of fabric. A tyre’s strength and load carrying ability were at one time indicated by its number of piles. Modern materials and manmade fibres such as polyester and glass fibre embedded in the rubber are much stronger than the cotton fibres originally used.

            Radial tyres give the impression that they have low inflation even though the air pressure is as recommended by the manufacturer. This is primarily because of the soft sidewalls. The physical difference between the radial and cross-ply tyres and in their behaviour on the road is governed by the difference in their individual carcass construction.

            Carcass is the rubber-bonded cord structure of a tyre integral with the bead and contains the inflation pressure. The radial ply has a stiffness and resistance in its tread area, so that in motion the tread in the contact patch retains virtually all of its pattern and grip.

            Radial tyres normally give twice as much mileage as cross-ply tyres and the difference in cost is not more than 30 percent sometimes even less and gives a marginally harder ride but is safer at high speed.

            Radials make the steering a little harder than cross-ply tyres, but provide better braking performance. The carcass of cross-ply tyres consist of textile cord ply fabric, but in a radial tyres it consists of steel belted cord laid substantially 90 {+0} to the centre line of the tread.

            Tyre consists of layers of cord called ‘plies’. Plies are shaped on a form and impregnated with rubber. There are two ways to apply the plies on the bias and radially.

                In bias type (ordinary) tyres the plies are criss-crossed. One layer run diagonally one way and the other layer runs diagonally the other way. The arrangement makes a carcass that is strong in all directions because of the overlapping plies. However the plies tend to move against each other.

            This movement generates heat, especially at high speed. Also the tread tends to ‘squirm’ or close-up as it meets the road. This increase tyre wears. Tyres with radial plies were introduced to remedy these problems.

            In radial tyres, all the plies run parallel to each other and are vertical to the tyre bead. Belts are applied on top of the plies to provide added strength paralleled to the bead. The radial tyre gives better fuel economy and lesser tyre wear.

        The source of the smell is most probably caused by bacteria and fungi feeding on organic matter in the rubbish. It will be more noticeable if the bin is in a warm and damp place.

            The smell will not always be exactly the same, but it will be more characteristic of the different organism than on the type of food they consume.

            The smell one gets from penicillin mould growing on an orange will be exactly the same as that from penicillin mould grown in a laboratory culture. It is pungent, characteristic and very common.

            Analyses of household rubbish have detected pathogenic bacteria, including Pasterurella pestis, the bacterium responsible for causing bubonic plague. So do not sniff too hard.

The Babylonians 3000 years ago used the sexagesimal system of numbering, which was based upon a multiplication of 6, instead of the decimal system which we now use. They divided the circle for example into 60x6 parts - the 360 degrees. Each degree in turn was divided into 60 parts was again divided into 60.

Claudius Ptolemy took this method of division from the Babylonians and called the first division of the degree the parts minutiae, or a small part. The division of this first small part he called the ‘pars minutiae secundae’ or the second small part, Ptolemy’s names became known as minutes and seconds.

Extracted from the book by title ‘Tick Tock’ compiled by I. Step nova, Prosveshcheniye Publishers, Moscow 1981, Page 36.The Babylonians calculated the number of days in a year as 360.

 The earth moved through the Zodiac in 360days as per their estimate and hence the division of the circle into 360 degrees, that is one degree per day. Time measurement is also based upon the sexagesimal system as there are 60 seconds to a minute, sixty minutes to an hour, 24 hours to a day, 30 days to a month and 12 months to an year and also 12 Zodiacal signs in astronomy.

The frequently used angular measurements in Geometry – 30’, 60’, 90’, 180’, & 360' are all multiples of six. The Gradian measure of dividing the quarter of a circle into 100 parts has not become popular. The angular and time measurements remain sexagesimal to this day even though the other two viz. Length and mass of the fundamental measurements have been metricated long back.

    Linear editing systems and non-linear editing systems are used in video and film editing. In Linear editing systems, edits to be made in a linear fashion, i.e. in 1-2-3 sequence.

One or more tapes containing the original footage are transferred (recorded) segment by segment onto a tape in a video recorder. In this process, the original segments can be shortened and rearranged, bad shots can be removed, and audio and video effects can be added.

 The source machine(s) contain the original footage and the edit recorder, which is controlled by an edit controller, is used to record the final edited master.

The person editing, using an edit controller to shuttle tapes back and forth to find the beginning and ending points of each needed segment. These reference points are then entered as either control track marks or time code numbers. The editor then turn things over to the edit controller, which uses the precise beginning and ending points that have been entered, to roll and cue the tapes and make each edit.

 Non-linear editing is a little like working with a highly sophisticated word processor; it allows segments to be inserted, deleted and moved around at any point in the editing process. In non-linear editing the original video segments are digitized (they are not in digital form when they come out of the camera) and transferred to computer hard disks. The editing system can access them in any order, almost instantly.

During nonlinear editing, a wide range of special effects can be added, including fades, dissolves, keyed in words and scene to scene colour corrections. Many audio enhancements can also be added, including sound effects.

Tear gas is a noxious gas. It is also called as war gas since it is used to disperse soldiers in a battle and all attacking mob. It is one kind of Lachrymator. Firing certain chemicals in artilleries or pen gun produces it. The chemical substance used is, alpha chloracetatophenone, a solid material or ethyliodoacetate a liquid material.

 The tear gas vapours cause irritation of the eyes with a copious flow of tears, spasm of the eye lids and temporary blindness. When eye is exposed to this irritant gas it creates a nervous reflex caused due to sensory stimulation.

As a result of this stimulation tear gland is induced to secrete copious tears, which flush across the eyeball. Tear gas also causes irritation of air-passages. In long continuous exposure there may be nausea, vomiting and blistering of skin. The effects are transitory.

Tear gas exposed persons should be removed to fresh air and they should wash their eyes with normal saline or boric acid solution. Weak sodium bicarbonate solution should be applied to the affected parts of the skin.

Intensity of the harmful radiations coming out of TV screen is strong near it and gradually falls In simple terms, the eye consists of a cornea (in the front), eye lens (in the middle) and retina (at the back). The space between the cornea and the eye lens is filled with an aqueous humour and that between the lens and retina is filled with a vitreous humour. Ciliary muscles hold the eye lens in its place and also change the shape (curvature) of the lens (to adjust the focus on objects) along with the help of the fluids.

 If one sits too close to the television or cinema screen, the eye Lens has to do more frequent focusing for viewing. Light rays from a near portion of the picture diverge and so the lens is curved more to focus on them. Simultaneously, the lens has to collect the light (coming more parallel) from more distant parts of the picture. This causes strain on the eye, and if practiced for long, can permanently damage the eye.

In addition, for optimum resolution of the picture and to reduce the level of radiation from the TV screen, we are advised to sit at a distance while watching the programmers.

In fact, the limit of resolution of the human eye is 1 mm at a distance of about 3 m. If one watches a TV sitting close to it one can see the picture elements (grains) which make up the picture. To see a clear sharp picture without eye strain, one must sit at an optimum distance so that the individual grains merge to form a complete picture.

 In a typical case, the main field of vision of the eye is defined by the vertical and horizontal viewing of 30-40 degrees; beyond which the vision is poor. Therefore, for comfortable viewing, a viewing angle of 10-15 degrees at the eye is optimum.

The width-to-weight ratio of the TV screen is kept as 4:3 because of the binocular vision due to the pair of eyes in the horizontal plane and the range of movement of both the eyeballs being less restricted in the horizontal plane as compared to that in the vertical plane. Hence, the best viewing distance for watching TV is 4-8 times the height of the screen (for a visual angle of about 10 degrees). For 51-cm TV, the minimum viewing distance should be 2.5 m. this minimum distance reduces eye fatigue by avoiding rapid movement of the eyeballs.

Also the light that falls on the eyeball comes directly out of the TV screen. Hence the with the distance from the screen.

So, to reduce exposure to these radiations, it is better to sit a bit far away. (In a theatre, the light falling on the eye is actually those reflected by the wall/screen and so the harmful effects are less.)

To reduce the strain on the eye, there must be some light in the hall. And this should be placed preferably above or on the sides of the TV to avoid any glare from the screen.