Page 1 :
tights ace, —_ T, Fas @ methods of charging a body. aa, , ur @ lightning, ae, , oy, ¢ OF exc @ safety measures during lightning. oa, "ndings irrence of earthquakes, 2 Eis ect 4 FE}, Ollow ing iction caused by earthquakes. Se, ens oF areata i, ® protection against earthquakes,, , become, , Ona stormy night, we often hear a loud noise of thunder, on the snd see a bluish-white flash of light in the sky (Fig. 13.1),, , ‘lusion Have you ever wondered what these are and how they are, qused? These are some natural phenomena that occur in, , What nature. Some other natural phenomenon are earthquakes,, , iting” tsunami, etc. You have already learnt about some of them in, the previous class., , letus read on to learn more about lightning and earthquakes., let us also find out how electric charges are linked with, , lightning., , , , Fig. 13.1: Lightning, , , , 13.1 ELECTRIC CHARGES ‘Do you know?, i Prot nd neutrons together form, Wealready know that atoms are made of protons, neutrons conics seamaen oe, , present in the centre. While 1, In orbits or shells., , , , nd electrons, Protons are positively charged, neutrons have, No charge and electrons are negatively charged. In the normal, stage, an atom has an equal number of electrons and protons, and it carries no charge. Hence, it is electrically neutral., Owever, any disbalance in the number of protons aad, “ectrons creates an electric charge. The charge on oe Y, * Positive if the number of protons exceeds the num| a o, *ctrons, If the number of protons is lesser than the number, ; ‘ons, the charge on the body is negative.

Page 2 :
13.1.1 Charging a Body, , An electrically neutral object can be charged by var, methods. Let us perform Activity 13.1 to understa, As, better,, , , , Activity 13.1 (Observe and list.), , , , To observe whether a neutral body can be charged or not, , * Take a balloon, an eraser, a plastic scale, an ebonite rod, a glass rod and a metal rod. You Can adg, more items to the list., , + Now rub these objects with different materials like a woollen sweater, a silk cloth, a polythene bag dry, hair, etc. and bring them close to small pieces of paper., , Note your observations in the table given below., Nature of charge induced in a neutral body, , , , Object leit) PNM elite ind Peterlee rea trier |, pieces of paper, Balloon | Polythene bag, dry hair, silk |, _ cloth, sweater | }, Eraser | Sweater | |, Plastic scale | Dry hair, sweater |, |, , , , , , Ebonite rod Sweater }, Glass rod Silk cloth | |, Metal rod Polythene bag, sweater |, , , , , , , , (i) Charging by friction: There is friction between two, bodies when they are rubbed against each other. This, produces an equal and Opposite charge in both the, bodies. Thus, we can say that friction is one method, of charging a body. Let us perform Activity 13.2 t, understand this method of charging.

Page 3 :
you have seen in Activity 13,2 4), at th, “at the comb attracts, , 1 dry | S, Y eaves after it was rubbed, because on rubbing, pl, © Plastic comb and, , m electrically,, , s ' cally. You can, , perform a similar activity by rubbing on inflated b;, ated, , , , qnall pieces of paper ar, , , , | witha woollen cloth. This happens, friction was produced be tween th, | woollen cloth which charged ¢}, , , , alloo, with a woollen cloth and taking it close to the wall, , i) Charging by conduction: If we touch a charged object, { re harged objec, , tectric charge will flow from, the charged object to the unc harged one, , fod. You ca,, , , , adg to an uncharged one, the, iy t : This method, 3 of charging a body is called charging by conduction, The body being charged will acquire the same charge, as the body charging it ., , (ii) Charging by induction: We can also charge a body by, a bringing a charged body near it, without touching it, The charged body induces the same charge that it has on, , the uncharged body. This method of transfer of charge, is called induction, , olythene b,, , , , {3.1.2 Transfer of Charge, , , , Wecan transfer electric charge from a charged object to a S, neutral object through a metal conductor. A device called, electroscope (Fig. 13.2) which is used to detect and measure Fig:'13.2: Electroscone, ] dectric charge is based on this principle. Let us see how it, | between two works through Activity 13.3., , ch other. This, e in both the, , , , , , , , , , , , , , (Make a model.), , ; one method, tivity 13.2 to, , To show the working of an electroscope, , * Take an empty glass jar with a wide mouth, * Take a sheet of cardboard big enough to cover the mouth of the jar., , 88 shown in the figure given alongside, , * Now take two aluminium foil strips of the dimensions, 4m = 1 cm., , * Hang them on the paper clip on the looped end., , * Place the cardboard sheet on the mouth of the jar as shown, in the figure given alongside:, , * Charge a plastic scale and touch the end of the paper clip, , it Observe what happens., oe find that the two aluminium foils at the bottom of the, , fepel each other., , , , An electroscope, , nd dry leaves, , , , , * Pierce a small hole in the cardboard sheet, * Open a paper clip from one end and insert it in the hole

Page 4 :
. ils repel each other bees:, , In the above sty Se kon re Sito saat Cats, , Oe of ae paper clip slightly with your ha, ee aoe they will come back to their or;, a ae ing of foil strips and touching the paper ‘, oaidsewl find that every time re touch the pa,, dip, the foil strips lose ae eS . 2 : :, ae ae ran a good conductoy We, ee o that foil strips get oe pting, process of transfer of charges from a charged object to the earth, is called earthing or oe), , , , , , , , , , , , , 13.2 LIGHTNING, , After having read about electric charges we can understang, how lightning occurs on a stormy night in the sky., , During the development of a thunderstorm there is an upward, movement of air currents while the water droplets move, downward. Due to these vigorous moyements, positive and, negative charges separate from each other. The Positive charges, accumulate near the upper edges of the clouds and the negative, charges accumulate near the lower edges. The positive charge, also collects near the ground. Although air is a Poor conductor, of electricity, yet when the magnitude of the collected charges, becomes very large, air is no longer able to resist their flow, Hence, negative charges meet the Positive charges producing, streaks of bright light and a loud sound. This streak of bright, , , , or is fixed :, top ¢, Bopper Pla, it flows tot, ‘ any damag, 2 Safety D, 4 ing lig], es, ee + nit, of the 00 mil, exceed Ee aaes its, Sand. Even this, How apart bricks,, the building., ightning can hit, i It can hit tt, need to take some, from lightning., e Donot stand |, and catches fi, e Do not rema, building or ay, closed. The m, - (by acting as, _ touch the me, © If you are o, , , , , , , , , , , , , , 13.24 Lightning Conductors, , S can also charge t F, , by induct; all buildings,, catch fre on. Sometj €s if the —, - To protect buildings, , Poles, wires and trees, harge is too heavy, they, from such damage, a lightning

Page 5 :
ductor is fixed on then, a at the top and a coppe; ,, , , , Kes 3, qhe copper plate is burie:, s, it flows to the earth thro, I, , , , ightning, , , , , Without, , , , , steam of ©, , , , (32-2 Safety During Lightning, , , , , , , , , , , , , , arg ©, ‘ge iol Positive ois, Beas oscpite putting ligh co «, hes. pes Being he fons © 6, a V jyildings catching fre due his spikes, a Lit gh magnitude of elect p, 8. g piihe high magnitude of electric current of copper, strip., , , , \ electrons, o> tepelled to|, the earth |, , , , 1,000 amperes), amperes) Lightning, , every cond, , , , tt to+ MS acceediNg 100 million volts an, , , , , , Ive path to the, , grrent divides itself to foll, sound. Even this divided current, , , , ough to ignite a f, , iow apart bricks, stones or concrete, or ir ure peor =, , , , ihe building 7, , , , I ne : > int, a | Jightning can hit anyone in the wrong place ong Fig. 13.3: A fightnin een, | time. It can hit the same place many times too. H ‘ i, a i nes too. Hence, we, an need to take some precautionary measures to protect our, r ‘otect ourselves, , , , , , Foplets move from lightning., , , Positive and sta, posit anc ¢ Donotstand under a tree. If the tree gets hit by lightning, , and catches fire you can be harmed., , , , sitive char, , ee Jo . not remain 2 an open place Take shelter inside a, rs ilding or a parked vehicle with all its doors and windows, erconductor | ~~ ¢losed. The metallic frame of the vehicle will keep you safe, cted charges (by acting as a lightning conductor). But take care not to, t their flow touch the metal to ayoid getting a shock, , s producing | * If you are out in the open with no safe place around,, , ak of bright, led electric, , squat down with your feet together and only let your feet, touch the ground (Fig. 13.4). This way you will reduce the, chances of letting electric current to pass from the ground, plugs | to your body., , * Do not use electrical appliances when light, hower because water, , electric gas 1, vith unlike | ning strikes, lightning | © Stay away from water. Do not takeas, , Te aa | isa good conductor of electric cur rent, he roof of any tall building, , h’s surface | * Donotgo on the terrace or on tl, , , , , , , Answer Orally, , , , eS | ‘he following. F, und tree | z (b) Earthing, vy, they ape conductor (d) Electroscope, , ightning