Light - PDF

for RRUITS necessary to see things in our surrounding&Bunjs asource gnghtenergywui the Earth. ight is aform of enerey that makobiects visiblp to our eyes/Ihere be darkncss around us in the absence of licht. We canno see things in the darkness. we etd a source of light to see the olbjects in darkne...

for RRUITS necessary to see things in our surrounding&Bunjs asource gnghtenergywui the Earth. ight is aform of enerey that makobiects visiblp to our eyes/Ihere be darkncss around us in the absence of licht. We canno see things in the darkness. we etd a source of light to see the olbjects in darkness. Let us understand some important aspects of light in this chapter LUMINOUS AND NON-LUMINOUS OBJECTS The objects can be classified as luminous or non-luminous, based on their ability to emit liglht of their own. (The objects which canemit their own lightare called luminous objects) For example, the Sun, star, candle, bulb, lamp, tube light and torch can emit light. So, we cancall them luminous objects. Sun Bulb Burning candle Torch Lumnous öbects We can see (The objects which do not emit light are called non-luminous objects)Achair, table, non-luminous objects only when light falls on them and gets reflected. etc., are some examples of non-luminous objects. The moon and planets book, plate, non-luminous objects. also do not have their own light. So, they are also Box Chair tree Bag Rock Non-luminous objects  SOURCES OF LIGHT to us are known as sources or make things visible us light artifGak Tne objects which provide can be categorised as natural and man-made or light of ight. The soures of Natural Sources of Light that are provided to us by nature are The soures of light light. The natural sources of l called natural sources of worms firefly, etc. are the Sun, stars, glow main source of light on the Earth. t plays a very Sun is the sustainabity of life on the Earth mportant role behind the would be darkness all around without the light of the There Sun is a natural source Sun. No life would exist and no plants and animals would for many natural processes such of light grow without it. I is essential plarnts and many others. as the water cyde, photosyrnthesis inand lightens it Light fromthe Sun reaches the Earth of it reaches the Earth's surface Stars produce their own light but a very little amount the stars. because of the long distance between the Earth and jellyfish, Some living things also produce light. These arehelps them fireflies and glow worms. The ability to emit light enemies and to attract their food (tiny animals), scare their Communicate with each other. Note that the moon does not have its own light. It receives light Moon reflects the from the Sun and reflects it on the earth. The moonlight that light of Sun ve see at night is the reflpcted light of the Sun. Artificial Sources of Iight he artificial or man-madesources of light are bulbs, fluorescent tubes, torches, lasers, mps, buming candles, etc. These objects do not produce light on their own. They ed,electricity electriccell/or other sources of energy to power them to emit light. Electric bulb Fluorescent tube Candle Some artificia ioht  -Do You Know? The study of the behavior, and properties of light is known as Qptics. PROPERTIES OF LIGHT The light we see everyday has Some properties. Let us learn about these. A Light is a beam of energy that moves in the form of a wave. Light travels at about the speed of 3,00,000 kilometers per second. Light traves-ir a£ompletely straight line until it hits any object. It travels in all directions when released from its source. Light can travel through Sun empty space (vacuum). When light rays fall on any object or surface, it bounces Light back. This bouncing back of the light is called the Reflected light reflection of light. Due to this property of light, the Reflection of light objects are visible to us. The light that we see from the Sun takes 8 minutes to reach us from Sun. Light travels faster in air, slow in water and slower in the glass.! When light passes through the air, water, or a glass, it Prism VIBGYOR bends and changes its direction. This bending of light to another direction is called the refraction of light, One example of refraction of light is splitting the visible light through the prism. When light passes through a prism, it bends and splits into seven Refraction of light constituent colour. These colours are termed through prism VIBGYOR (violet, índigo, blue, green, yellow, orange and red). 9  Practice Time Match the columns. A B 1. Natural sources of light a. Sun, torch 2. Artificial sources of Fb. Water, rock ligh 3. Luminous object_ e. Travels in a straight lines t4. Non-luminous objects d. Sun, stars Candle, torch S5. Light, TRANSPARENT, TRANSLUCENT AND OPAQUE OBJECTS not pass though Light can pass through solid, liquid and gas. However, light does completely, some allobjects completely. Some objects allow light pass through them allow light to pass through them partially and some do not allow light to pass through them at all. Based on the amount of light that an object allows to pass through them, objects are classifed into transparent, translucent arnd opaque objects. Transparent Objects: The objects that allow light to pass through them completely are called transparent objects. We can see through them completely. For example, water, air, clear glass, cellophane paper, etc. Translucent Objects: The objects that allow light to pass through them partially are called translucent objects. Clear glass is transparent We can see partially through them. For example, tissue paper, buter paper, oily paper, muddy water, sunglasses, frosted glass are some translucent objects. Opaque Objects: The objects which do not allow light to pass through them are called opaque objects. We cannot see Frosted glass is anything through them. For example, translucent wood, cardboard, brick wall, metal, book, pern are some opaque objects. The mirror is also an example of opaque object, It does not any light to pass through it. When light falls on a allow mirror, it is reflected by the metal coating. Amirror forms images of the refloction of light. because Cardboard is opaqu 40  Activity-1 light to To know that the transparent and translucent objects allow pass through them or not. Take a clear glass tunbler. arnd butter paper. See across them one by one. Which of these are allowing you to see the things through them? Discuss with your friends about this observation. SHADOWS We have learnt that the light travels in astraight line. When an opaque object blocks the path of light,a dark patch called shadow is formed on the surface at the other side of the object. Shadow is adark patch fomed when an opaque object obstructs the path of light. The translucent objects can only do partial blockage of the path of light. Thus, the shadow formed is very faint. The transparent objects never obstruct the path of light. So, they do not form any shadow. The shadows are formed because light does not bend around the corners while travelling on th¿ir path Conditions for Shadow. Formation Source of light A shadow formation needs the following three conditions: Opaque öbject A source of light, such as Sun, bulb, or candle Shadow An opaque object Ascreen or surface behind the object Conditions necessary for Shadow can form only when all the given three shadow formation conditions are available. The colour of the shadow is always black. Ashadow has the following properties: It is always formed on a surface or a screen behindthe object. A shadow from a strong source of light is sharp, whereas shadows from a w source of light is blurred. It does not have a fixed size. A shadow is longer in the morning and evenin shorter during mid-day. Think and Answer Why do the shadowS not form at night or in dark room? Size of Shadow Morningsun Sun at afternoon The size of the shadowdepends on the time of the day. Visit a Evening garden at different times on Sun a sunny day - morning, mid shadow formation day and evening. Observe the Position ofSun and morning andeevening. shadow of a tree during these tree arelong inthe thattheshadows of shines brightly overhead. times. You will notice theSun veryshort when the shadow is At mid-day, ENERGY CONSERVATION OF LIGHT energy for various activities. a form of energy. We use this purposes, But, at night that light is various We have learnt there is sunlight and we use it for electricity or batteries During day time, sources need sources of light. These artificial sources of light energy we use artificial minimize the use of artificial provide us light. We should only as much as requiredis called to saving or using a resource light energy n conserve energy. The efficiently conserve to The given below simple ways can conservation. our day-to-day life: instead of artificial sources of light. It is the Sunlight should be used in day time. energy. best way of conservation of light solar heaters which conserve surnlight solar panels and There are solar cookers, other activities. and use it for cooking, heating and install solar panels on the roof of your house. Suggest your parents to Solar heater Solar cooker Solar panel methods Some energy conservation Dry clothes under sunlight instead of drying in the washing machine or in the " running fan. Cover the pans with lids while cooking. It saves fuel. Turn off the lights as you leave a room, unless you are coming straight back. 42  & Take chargers out of the wall socket. Never leave them switched on, whether they are for our mobile, lapop, or any other device, Theyuse power even when the device is not charging. 6 Walk to neighbourhood places or use public transport. If you useair conditioner, get it serviced to ensure that it works efficiently. IKhot weathe? parkin theshade to stop your car from overheating. Unplug computers, printerS and kitchen equipment after every use. Usèstairs rather thanthe lifts. Encourage others also to do so.. Use glass onwindows to allowsunlighttoenter the house. Practice Time Match the columns. A B 1. Transparent object a. Book 2. Opaque object b. Conservation of light energy 3. Translucent object Lc. Clear glass 4. Shadow formatior, d. Butter paper 5. Solar cooker e Source of light Difficult Words Luminous objects : Objects that emit light of their own Non-luminous objects : Objects that do not have light of their own Transparent objects Objects that allow light to pass through them Translucent objects : Objects which allow light to pass partially completely Opaque objects : Objects that do not allow light to pass through them Reflection through them :A phenomenon of bouncing back of light from the surface of an object A Summing Up The objects can be classified as luminous or There are two sources of light - natural and non-luminous objects. man-made artificial.. or Transparent objects allow light to pass through them and we can see through these objects. Translucent objects allow light to pass through them partially. Opaque objects do not allow light to pass through them. 43