Light (Tell Me Why 85) Lead, Kindly Light From the beginning of time, Man has been fasci nated by the phenomenon of light Our forefathers believed that our eyes sent out light so that we could see t.
Lead, Kindly Light From the beginning of time, Man has been fasci nated by the phenomenon of light Our forefathers believed that our eyes sent out light so that we could see things Yet, there were many enquiring minds that were not satisfied with this explanation The questions raised by them triggered the study of light, and this eventually evolved into the science of Optics The trailblazers in the field of Optics identified light as a form of energy that travels at the incredible speed of 299,792, 458 metres per second in a vacuum! It is notjustthe speed of light that is amazing - every aspect of it captivates, entrances, and boggles the mind As Diwali, the glorious festival of lights, approaches, get ready to be transported into the wondrous world of light, in this exciting issue of Teil Me Why �-t;;;� - To subscribe to Tell Me Why online, logon to www.manoramaonline.com/subscribe • " For subscription enquiries: Please call our toll-free number - 18004255002 (between am & pm on working days) M.M Publications Ltd., P.B No 226, Kottayam, Kerala, India Pin·686oo1 Phone:0481·2563721 ·22 ,23 Fax: ++91· 481·2564393 Email: subscription@mmp.in childrensdivision@mmp.in NEW DELHI: Malayala Manorama Co Ltd Andhra Vanitha Mandali Building, 2, Azad Bhavan Road, Indraprastha Estate, New Delhi·110 002 Phone: 011·23379718, 23379719, 23379720 MUMBAI: Malayala Manorama, A- 404 Marathon Innova, A Wing 4th Floor, Lower Parel (West), Mumbai - 400 013 Phone: 022 - 39495969,24900844, 24901331 KOLKATA: Malayala Manorama, 14 Parasar Road, Near lake Market, Kolkata - 700 029 Phone:033 - 24198233,24198048 PATNA: Malayala Manorama, 608,Jagat Trade Centre, Frazar Road, Patna - 800 001 Phone: 0612 - 2233809 JAIPUR: Malayala Manorama, C/o Royal business Centre,Usha Plaza, Near JaipurTower,M.I Road,Jaipur - 302 001 Phone:0141 - 2368360, Mob: 94616 28972 HYDERABAD: Malayala Manorama, C/o Dr B.C Mathur, 8-2- 62911/B, Road No.12,Banjara Hills, Hyderabad - 500 034 Phone: 040 - 23314168, 23324692 BENGALURU: Malayala Manorama, No 132, Kantha Court, 3rd Floor, lal,Baugh Road, Bengaluru- 560 027 Phone:22247735 136 CHENNAI: Malayala Manorama, Unit B III Floor, 23, Spur Tank Road,Chetput, Chennai-600 031 Phone: 044 - 43181405 COIMBATORE: Malayala Manorama, 101,Sunshine Buildings,1056, Avinashi Road,Coimbatore - 641 018 Phone:2241911 / 2245470 LUCKNOW: Malayala Manorama, B-1657, Indira Nagar, Lucknow-226 016 Phone: 0522 - 2341576 CHANDIGARH: Malayala Manorama, H No 2252, Ground Floor Annexe, Sector 21- C, Chandigarh -160 022 Phone:0172 - 2724699 Mob: 09417310727 BHOPAL: Malayala Manorama, Plot No,161,Gopal Bhawan, Zone 1, M,P Na9ar, Bhopal Phone: 0755 - 2557937 THIRUVANANTHAPURAM: Malayala Manorama, P,B No, 160, Thampanoor East,Thiruvananthapuram695 001 Phone: 2328198 KOCHI: Malayala Manorama, P.B No, 5008, Panampilly Nagar, Kochi - 682 036 Kerala Phone: 04a4 - 2316285 What is light? W e all know what light is We also know that the Sun, fire, bulbs, and glowworms all give us light But what exactly is light? Light is a form of energy that which we can see It is made up of billions of tiny particles called photons These photons travel from one place to another in waves The light that we can see consists of photons that move at a wavelength that makes it visible, and is known as visible light Tell Me Why Visible light is actually made up of different colours Among the different photons that are in visible light, the ones that have the longest wavelength look red to us, and the ones that have the shortest wavelength look violet to us Red, green, and blue are the primary colours of light Mixing them in various ways will make all other colours, including white Isn't that amazing? light I th ink this is the time to recharge my torch The Sun and Flowers Why was the Sun considered a God in ancient times? P eoPle through the ages have worshipped the Sun as the source of light, and therefore, as the source of all life Our ancestors realized that if there was no Sun, the Earth would be plunged in perpetual darkness It would be unbearably cold, and all the water on Eart h would freeze up They had no clear idea of how the Sun produced light, nor why it moved throughout the sky They did under stand however, that without the Sun, life would not be possible Ancient civilizations were primarily agricultural, and depended on the Sun for life, and their crops Therefore, it is no surprise that they worshipped the Sun as a God Our ancestors observed that leaves and flowers of certain plants often turned to follow the movement of the Sun in the sky during the course of a day This plant, known as 'sunflower'in English, was used in ancient times to worship the Sun by certain civiliza tions of Central and South America Why is light responsible for life on Earth? W ithout light, there would be no life Plants need light to produce food through the process known as photosyn thesis Light is the only way for plants to get the energy to grow Animals depend on plants for their food, either directly, or indirectly Human beingstooeat plants, oranimals that eat plants Without light, all the plants on Earth would die - and animals and people would be left without food, and would die too Light is also important because it gives the Earth the warmth needed to support different forms of life Grow up, g row up baby Some living creatures like fireflies create their own light Others, like Man, have learnt to create artificial light when natural light is not available Light lets us see things Without any light, we would see nothing at all How did Man make light? O Magic Flames Have you heard of the term 'will o'the wisp'? It refers to a flame that is often seeing moving by itself over marshy areas - quite an eerie phenomenon There is a simple explanation for this however The rotting plants in a marsh or swamp produce a gas called methane, while the remains of rotting animals produce a gas called phosphine When phosphine meets the air, it causes a spark, and this spark ignites the methane that is present, creating a naturally occurring flame The flame moves quickly over the marsh as the methane catches fire in different places ne of the biggest achieve ments of Mankind was when our ancestors learnt how to make fire in the distant past Early Man depended on the Sun for light during the day, and on fire for light at night Later, people learnt that by rubbing two stones or two pieces of wood together, they could produce a spark This discovery proved to be a turning point in the history of mankind, for it provided early Man with the knowledge to start a firethat would provide him with light, warmth, and safety from wild animals A l ight dinner is ready Tell Me Why Why is sunlight white, while a rainbow has many colours? T he light from the Sun is really a mixture of many different colours or wavelengths of light The wavelength is simply the distance in which a wave repeats itself Red light has a long wavelength, while violet light has a short wavelength The light that we can see, or visible light, is actually made up of different wavelengths that we see as red, orange, yellow, green, blue, indigo, and violet light These colours gradually merge into one another, and the mixture produces white light As white light passes through droplets of water in the sky, the light is refracted or bent The longer wavelengths of light are refracted more than shorter wavelengths This causes the colours to be separated as they pass through the raindrops The result is the rainbow of seven colours that you see in the sky! RADIO WAVES MICROWAVES INFRARED VISIB RADIATION LIGHT What are eledromagnetic waves? T Light to Lead In ancient times, people made fires at the edge of the water to warn boats of.s!.angerous rocks and shores Later, light houses were built to serve this purpose The first proper lighthouses were built by the pharaohs of Alexandria he heat produced by the Sun travels from the Sun to the Earth via waves known as electromagnetic waves These waves can vary greatly in their wavelength Electromagnetic waves possess both electric and What is the speed of light? W e know that light travels in waves These waves are not of the same wavelength Some wavelengths are longer than others However, all waves move at exactly the same speed in a vacuum When we talk about the speed of light, we are referring to the speed at which light Tell Me Why Glowing Iron Rod A l l that gl itters is not gol d , but now, a l l things can glow Why things glow when they are very hot? W hen heated an i ron ba r is a very high to temperature, it i nit ially g lows red, a n d then a s its temperature rises, it glo ws white This process is ca l led inca ndescence I nca ndes cence is heat made visi ble when heat energy tu rns i nto l ig ht energy Why d oes this happen? \O Uf � �� '-i 84 RADAR The word RADAR is the short form of the oo;f(' term Radio Detection and Ranging A radar scanner emits very short radio waves Objects in the path of these waves send back echoes that are picked up by the scanner Tell Me Why Everything around us g ives off both heat and waves of l ig ht called infrared light, which we can not see Even things that we think of as bei n g very cold, l i ke a n ice cube, g ives out some heat As a n o bject becomes wa rmer, its atom s emit much more wave energy, and the waves it produces become shorter and shorter If it is warmed enough, the shorter waves wil l g ive off visible l ight as the object starts to g l ow When an object heats u p, first it glows red, a n d then wh ite when it becomes rea l ly, rea l ly hot X�Rays � - X-Rays are waves of light we cannot see, but which carry more energy than visible light They can pass through the soft parts of our body, but not through bone X-Rays are used to show doctors what is going on inside your body, like whether you have fractured a bone or not Sneha Rao To put it in a n utshel l, everything glows, not j ust hot objects Most things glow in the frequencies, i nfrared which h u ma n eyes can't see When an object gets hot enough, it g l ows in the visible frequencies, which l i g ht we c a n see, a n d then we say that it is 'red- hot' or 'wh ite-hot'! Light 85 hy is UV light hannful to us? U ltraviolet or UV light has a shorter wavelength than visible lig ht, so we can not see it U ltraviolet radiation possess h igher energy than visible lig ht, and are respon s i ble for causing our sunburns UV light can (osmic Rays cause some type of skin cancers also UV Cosmic rays are highly energetic particles that originate in outer space They are born from clouds of gas surrounding the ancient and massive explosions of distant stars, and they slam the Earth's upper atmosphere at very high speeds s u rface of water, and from w hite surfaces UV Light 86 light can be reflected strongly from the suchas snow,and ca n ca usesnow-bl indness It is a lways better to wear protective gogg les or sung lasses that filter out the UV l i g ht to prevent serious eye damage Though some UV rays from the Sun penetrate Earth's atmosphere, most of them are blocked from entering by various gases l i ke ozone However, increasing damage done to the ozone layer in the Earth's u pper atmosphere means that more and more UV light is now reaching the surface of the Earth This is dangerous to us How plants use UV light? Some i n sects l i ke bees see a very d ifferent spectrum of colou rs from what we see, and they ca n see UV l ight Bees play a very important role in nature, for they tran sfer pollen from one flower to another These flowers are brightly a colour that bees ca n't see This is attract where UV light plays a role The red i nsects l i ke bees Some flowers reflect UV lig ht- which is a of them are a bright red, colour that is visible to the bee The coloured to bee is then attracted to the red flower, a n d flies to it to d ri n k its nectar- and i n Not a spacesuit, it's a UV protection suit t h e process, get some pollen on its body that wil l be tra nsferred to a nother flower When some materials a re lit by UV lig ht, they emit a fl uorescent g l ow Some such chem ica l s a re used in l a u n d ry detergents as wh iteners They bind to the natural fibres in clothes, and make them look brig hter i n s u n l ig ht U ltra violet light is u sed to ki l l bacteria, reactions, and hasten to chemica l identify some fluorescent mi nerals UV l i g ht can also be u sed to show things the h u man eye can't see, which makes it very useful for forensic scientists light 87 Why is infrared light useful to us? Slightly more than h a lf of the energy from the Sun a rrives on Earth in the form of infrared rad iation, and nearly everything a round us g ives off some form of infrared lig ht I nfrared l ig ht has a wavelength that is a l ittle longer than that of the red light than we can see, and it is not visible to human eyes However, many animals l i ke the piranha fish that live i n the Light and Gravity Albert Einstein also put forward the idea that light can be bent both by refraction, and by gravity Light ordinarily travels on a straight line path but it will follow a curved path if it passes through a strong gravitational field This is called 'curved space,' and this explains why light becomes trapped in a black hole Radha Nair 88 m u rky waters of the Amazon River, have the ability to d etect infra red l i g ht.Somei nsectstoo have a ntennae that can detect infrared light, and this lets them see in the dark Today, research scientists a re developing devices using infrared light that have many uses, both for the m i l ita ry, and in everyday life N i g ht-vision near-infrared devices using active i l l u m i nation a l low Infra Red Light Tell Me Why Piranha Fishes people or animals to be observed without the observer being seen Infrared l ig ht is used i n i n du stria l, scientific, and medical a ppl ications So, though infrared l ight or 'IR' is just out of nge of what the h u m a n eye can d etect, we can stil l use i nfrared l i g ht to see things! Gamma Rays Gamma rays have very short wavelengths They carry very large amounts of energy, and can penetrate even metal and concrete High levels of these rays are very dangerous, and can kill living cells Because gamma rays can kill living cells, they are used to kill cancer cells without having to resort to difficult surgery Gamma waves are generated by radioactive atoms and in nuclear explosions nothing can move faster than light in a vacu um, and that the speed of l i g ht i n a vacuu m is always the His same work revol ution ized the way scientists viewed the world, and had a tremendous i m pact in the field of physics Einstein on hisfirst US visit Why is the Theory of Relativity related to light? especially in studies on l ig ht What are photochemical reactions? I n March 1905, Al bert Einstein, one of A ny reaction that the g reatest scientific minds of a l l time, takes place only in expla ined the Quantum Theory of Light the presence of light Accord ing to this theory, l i g ht exists as is known as a photo tiny packets, or particles, which he cal led chemical reaction photons Along with another scientist, The may Max Planck, Einstein proposed one of the visible lig ht, infrared light be most revol utionary idea s i n twentieth radiation, or century physics- that we l ive in a u niverse violet rad iation b u i lt out of tiny, d iscrete c h u n ks of energy and matter Many photochemical Later, in 1905, he pu blished his Theory u ltra reactions ta ke place in nat u re, and the of Special Relativity In this theory, he best example is extended Galileo's principle of relativity, photosynthesis In so that, it accou nted for the constant photosynth e s i s, speed of light Einstein saw light a s both a g reen wave and a particle He showed that food using s u n l i g ht 90 p lants make Tell Me Why to combine carbon dioxide and water Therefore, plants convert light energy i nto the chemical energy of food P hotochemical changes a re a lso part of industrial processes, such as the formation of images in photog raphy When a picture is taken, some of the si lver salts on the photogra p h i c fi l m a bsorb l ig ht, a n d chemica l ly change i nto metallic si lver, which produces a dark image on the negative when the fil m is developed We know that light is made of photons trave l l i n g at d ifferent wavelengths which make u p d ifferent colours of the spectrum But not all wavelengths wil l trigger a specific photochemical reaction For example, a photon of violet l i g ht has highest frequency, and hence, the hig hest energy Hence, a reaction which is initiated by violet l i g ht may not be i nitiated by red, blue, or other wavelengths of lig ht Another inter esti ng fact is that some su bstances not react directly when exposed to light, but the a d d ition of a nother substance will trigger a photo c hem ical reactio n How is digital photography different from film photography? In a fi l m camera, points of light are detected, and each point is recorded by a g i n of chemica l material on a fil m that is lig ht-sensitive The fil m can be processed in a l a b, a n d t urned into negatives, prints, or tran sparencies The resulting image can be put in a book, fra med and put o n you r desk, or j u st kept in a box In a digital camera, there is no fi l m Poi nts o f l i g ht ca l led pixels a re detected using an a rray of l ig ht-sensors known a s photo-detectors Each point represents colour a n d i ntensity The collection of pixels forms an i mage that is saved to some kind of electronic medi a l ike a flash Why arecompadfluorescent bulbs different from incandescent bulbs? I ncandescent bulbs are the standard type of bu l bs that were most common till some years back I ncandescent l ight bulbs are made of g lass, and are rou n d in shape They work by heating a tungsten filament, orwire, u ntil it glows This is what produces the l ight that you see Unfortunately, 90% of the energy used to generate that l ight is wasted as heat, making inca ndescent bulbs a very inefficient way to l ight your home I n stead of a g lowing fi lament, CFLs 92 Tell Me Why card, mag netic disc, or optica l d isc The resulting file Digital Camera can be read by imaging software on a compute r , and the image can then be printed To s u m u p, film cameras use rolls of fi lm that have to be developed Digital cameras use memory to store the images, and can be uploaded to you r computer or ipod, so that you ca n see the picture d i rectly mercury tests, they bu rned brightly for va pour housed within a tube contain through the mixture, the gas 0,000 hours, whereas sta ndard 800 to ,500 hours C F Ls use signifi cantly less energy 75 percent gets excited, and it produces less energy tha n i ncandescent cu rved argon in and d ifferent s hapes When a n electric cu rrent passes bulbs bu rned for j ust - u ltraviolet light The u ltraviolet light bulbs Th is means that by lig ht, using CFLs, you are not only in turn, stimulates a fl uorescent coating pai nted on saving the i n side of the tube As this helping the environment by coati n g a bsorbs energy, itemits red ucing energy consumption visible light and CFLs last a longer time than i ncandescent bulbs I n some Light electricity, preventing but a lso g reen house gas emissions that contri bute to gl obal cli mate change 93 What is sunburn ? I f you stay out in the S u n for too long, your skin may become red or da rk, and even become painful and swollen This is known as s u n b u rn, and other symptoms may include fever, chil ls, na usea and vomiting, weakness and symptoms of shock Why does this happen? The reason is that s u n li g ht has u ltraviolet rays, and over- exposure to u ltraviolet rays is rmfu l to both our skin and our eyes As you near the tropics, the S u n 's rays a re more i ntense and more d irect, so the risk of s u n burn increases- and so does its severity So, it is always better to wear a 94 Tell Me Why Raman Effect The great Indian scientist Sir C.V Raman put forward a new theory on the scattering of light, for which he won the Nobel Prize in Physics in 1930 His theory, known as the Raman Effect, states that the wavelength of light changes after passing through a medium, and being deflected by the particles of that medium hat, or hold an um brella and slather yourself with sunscreen lotion when going out d u ring the Winners ofthe GK Contest -3, Freedom Fighters- held in the August issue ofTell Me Why Anjali Pakde 3,Ganesh Nagar, Nandewar Road, Bharuch, Gujarat Saumay Shikher Raj Uo Sri Hardeo Prasad, Menka Bhawan; Bampass town, B Deoghar, Jharkhand Varad Kumar 415, Gaur Galaxy, Sector-5 ,Plot-5, Vaishali, Ghaziabad, Uttar Pradesh Ananya Uo Prabhash Kumar, Naka No.5 Darbhanga, Bihar KanishakarY 7/1 , ' Avenue, Ashok Nagar Chennai, Tamil Nadu GK Contest -3, Freedom F ighters ANSWERS Dadabhai Naoroji Chandrasekhar Azad Bhagat Singh Captain Lakshmi hottest part of the day Light 95 Here's a contest in which our readers have to identify five SCIENTISTS, from the pictures given here All you need to is send us an email naming each person with the proper number (PLEASE GIVE YOUR POSTAL ADDRESS ALSO IN THE EMAIL) P OlO QUIZ You are also welcome to send your answer by post Five winners will be awarded prizes In case there are more than five correct entries, the winners will be chosen by lot Last Date to receive entries: October 25th If you are sending your entry by post, superscribe this on your envelope M.M Publications Ltd., P.B No 226, Kottayam, Kerala, INDIA Pin - 686 001 Question of the Month I ionder Why does an electric bulb make a bang when it is broken? IhV� of a n electric bulb and the consequent Have you ever noticed the brea ki ng bang? Th is sound is produced by the air surrounding the b u l b The i nside of an electric bulb is vacu u m So, the pressure i nside is lower than that of the outer atmosphere When the bulb is broken, a i r rushes in at h i g h speed from a l l sides to fil l up the vacuum The sudden surge of air produces a bang An electric bulb produces light when its fi la ment is heated at a high tem per ature The vacuum i nside the bulb prevents the fi lament from oxid izing with a i r Send us your questions E mail: childrensdivision@mmp.in • Alwin George MANORAMA TELL ME WHY - LIGHT Editor: Ammu Mathew Editor-in-(harge: A.V Harisanker * Printed and Published by V Sajeev George, on behalf of M.M Publications Ltd, P.O No 226, Kottayam - 686001 at M.M Publications Ltd, P.O No 226, Kottayam - 686 001 and Malayala Manorama Press, Kottayam · 686 039 and published from M.M Publications Ltd, P.O No 226, Kottayam - 686001 * Responsible for selection of news under the PRO Act ... firethat would provide him with light, warmth, and safety from wild animals A l ight dinner is ready Tell Me Why Why is sunlight white, while a rainbow has many colours? T he light from the Sun is really... the speed of light was officially approved to be 299,792.458 kilometres per second 12 Galileo Tell Me Why The biggest object that bounces sunlight is the Moon Though we talk of moonlight, the Moon... when they are in sunlight Why does this happen? Sometimes ,objects are able to block light An object through which no light can pass is called opaque An example is our body Since light cannot pass