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LIGHTNING Batt, Lightning is caused by electric charge. Therefore, to learn abo, , i i e and how they behave. : :, learn a few basics about electric charg ia idipee, , -)._f -7, 47 EL OUR brid Fig, ELECTRIC CHARGES Ae ne AL IVOT, , All matter is made up of atoms. Every atom is madéup of positively ae es, negatively charged particles, and neutral particles. The positively charge Oi all an, atom are called protons. The negatively charged particles are called electrons: Sually, the, atom as a whole consists of an equal number of positive and negative charges, and the, atom is electrically neutral. If, however, the, , charges are not balanced, the atom will have an, . Les ' A, eleeniy charge (positive charge if protons a e, more in number than electrons, and negative, charge if electrons are more in number than, , protons). {a) Like charges repel each other, , If two objects having the same type of charge, _, , ightning, we have to first, , , , (i.e, Positive-positive or negative-negative) are, brought close together, they repel each other, (ie, push each other away) [Figs. 14.1(a) and, , , , (b)]. If, however, the two objects are oppositely {D| ks charges sepel eachy ether, charged (positive-negative or negativePositive), they attract each other (ie., pull site, towards each other) [Fig. 14.1 (c)]. Therefore, we, can say like charges repel each other and unlike ( ig, (c) Unlike charges attract each other, , charges attract each other., , - Fig.14.1 Electric charges, Charging an Object, , Most objects around us are electrically neutral because they have equal number of positive, and negative charges. An electrically neutral object can be charged (i.e., given an electric, , charge) by using any of the following methods., Charging by friction This kind of charging is, , done by rubbing one material with another. guns : cE, The most common examples are rubbing glass ‘j, with silk, and ebonite (a kind of hard rubber) “Hit eee, with wool. When a glass rod is rubbed witha ¥ e a, piece of silk, negative charges are transferred Ss, from glass to silk. The glass rod is, therefore, Le me, , +e . * iece of sil, left with a positive charge and the piece of silk Fie 142 Wheh denis devices ans, acquires a negative charge (Fig. 14.2)., , piece of silk, both objects get charged

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if an ebonite rod j, _jlatly:! 'S tubbeg yw:, g(t negative charges are tran €d with, , ie ‘ece of wool to the ebonit an from, ie “ite rod becomes negatively chia h, , Pe piece oF WOO! becomes pealtiey, nae! (Fig. 14.3). ely, , , , ++, Fig,, , iB 14.3 When an ebonite rod is rubbed with a, , Plece of wool, both objects get charged, , Activity, , , , , , , , Aim: To use the ‘method of chargi, objects can be charged by this, , , , , , , , , , , ‘ eraser, plasti 5 7, small bts of paper, a metal clip, P’astic pencil sharpener, plastic pen cap, plastic comb,, , sastti6e @ small hand towel or Napkin, and tabletop, , 4. Cut out the bits of Paper into small Squares having 2-4 millimetre sides., , . Take the i, 2 ae = plastic sharpener, plastic comb, and plastic pen cap one by one, and, ol ch of them, close to the bits of Paper and see what happens., , 3. Next, spread out the hand towel or napkin on the tabletop and rub the eraser on it, vigorously., , 4. Thereafter, bring the eraser close to the bits of paper. See what happens now., Repeat this process with the plastic pencil sharpener, plastic pen cap, plastic comb, and metal, clip. What do you observe?, Note: The composition of the materials (hand-towel or napkin) is not standard and may vary, from place to place. So please try a few materials till you can charge these objects (plastic, sharpener, plastic comb, plastic pen-cap, etc.)., Observation: You will observe that before rubbing, the eraser, sharpener, comb, pen cap, and, metal clip had no effect-on the bits of paper. However, after rubbing, the plastic eraser, plastic, sharpener, plastic comb, and pen-cap attract the bits of paper. However, the metal clip does, not attract the pieces of paper even after rubbing., , , , i be charged by the method of, i de of rubber and plastic) can, Con + Some objects (mai 2, mange (made of metal) cannot be charged by this method

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“ae, , Charging by conduction An object can also be charged by Be See ee body,, For example, if we take a charged glass rod and touch a metal o . ae s etal :, object will also become charged. This Is called charging by Se eith ont : i of, , the charge acquired will be the same as that of the charging body/In , a * i. metal, object will also get the same nature of charge (positive) as the glass rod (Fig. 14.4),, , , op phd, NVA aearegidiccieind GA I, , +, €, , > % — _ Glass rad (pasitive}, +, , , , , Glass rod (positive) ——_____» i, , , , , Metal, object (neutral) te,, Metal object, (positive), (a) (b), **Fig.14.4 Charging a metal object by conduction, Activity, , ‘2, , , , Aim: To observe how charges behave when they are brought close to each other, , Materials needed: Two Plastic straws, eraser, plastic sharpener, glass bottle/tumbler, piece of, silk, wool, , Method: Charge one plastic straw and keep it in the glass bottle/tumbler. Charge the second, Plastic straw, eraser, and Plastic sharpener, one after the other, and bring them close to the, , | Plastic straw in the glass bottle. What do you observe?, , i Observation: You will see that when we bri, , ing charged objects close to One another, they are, either attracted towards eachother or are, , repelled from each other., , Charging by induction \n charging by induction,, , charging is done without the charged body touching, , the object that has to be charged. For example, a, , charged glass rod is brought close to a metal object, but, 63 does not touch it (Fig, 14,5),, , , , Fig. 14.5° Charging a metal object by induction

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y, , |, , ger of Charge, ye Knob, i charge can be transferred from, another through a metal con, , a charged, , ly, ducto, 1a pat works on this principle is the elects, , e, f , used to detect and Measure electric ¢, fi! sats of 040 very thin metal strips (called, , scope,, harge) Metal, , leaves, , , , of! hi leavés,, is isethey are very thin) connected to a metal, ye metal rod (Fig. 14.6),, , _ishow it works. Fig. 14.6 An electroscope, , : acharged object is made to touch the knob of the electroscope. Repel re2anJ5,, , ythe charge is transferred to the thin metal strips through the metal rod. ti ] 3 zeyat i, , rremetal strips repel each other (because they have similar charges) and separate from each, ~ gher The electroscope can, therefore,, , be used to checkifa body carries a charge (Fig. 14.7)., pena charged object comes in contact with a body, , -pichis not charged, electric charges jump from, , gecharged body to the uncharged body till the E ', , ; garges on the two bodies are equalized. This process -:, , \yeferred to as discharging |When a body comes in, , ntact with the Earth, either directly or indirectly,, , ' tenthe charges are discharged to the Earth. This is, , ‘ led earthing. Earthing is both important and useful, , | tous. You would have heard the word ‘earthing’ being, , | used many times in your house\Chis is because most, , / eectrical appliances and the mains of the house are, , _ ‘arthed’ (i.e,, connected to the Earth) for our safety,, __ that we do not get an electric shock Fig. 14.7 Detection of electric charge, , , , , , Negatively, charged, rod, , Electrons flow, downwards, , , , , , , , MECHANISM OF LIGHTNING, , Ughtning occurs because of a massive electric charge flowing from cloud to cloud, from, , one part of the cloud to another, or from a cloud to the ground. Scientists are not very sure, Sactly how this happens, but thunderclouds carry electric charges, and these charges, “*parate within the cloud. The lower portion of a cloud generally carries negative charges, and the upper portions carry positive charges. These charges keep building up. Normally,, “arges do not flow easily through air. Air is an insulator, but when a huge amount of, “alge builds up, the insulating property of air breaks down. Nearby air molecules are