Glass rod, fur or cat skin, woolen cloth\u00a0\u00a0\u00a0 <\/strong><\/td>\nSilk cloth ebonite rod Amber rod plastic, rubber<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n\n\n\n4. Conductor, insulator & dielectrics<\/u>:-<\/strong><\/p>\n\n\n\n Conductor:- <\/strong>A substance which can be used to conduct electric charge from one place to another place is called conductor. Silver is the best conductor. Other examples are copper, aluminum, iron mercury, earth, human body etc.<\/p>\n\n\n\nInsulator:- <\/strong>A substance which cannot be used to conduct electric charge is called insulator<\/p>\n\n\n\ne, g :- glass, rubber, plastic, ebonite, mica, wax etc.<\/p>\n\n\n\n
Dielectric:- <\/u><\/strong>Dielectric are those insulators which does not conduct electricity but on Appling external electric field charge induces on it e, g:- glass rod & paper acquire charge on rubbing.<\/p>\n\n\n\n 5. Gold leaf electroscope ( G L E )<\/u><\/em><\/strong><\/p>\n\n\n\nIt is a device which is used for detecting an electric Charge &identifying its polarity. It is consist of a vertical conducting rod passing through a rubber stopper fitted in the mouth of glass vessel. Two thin gold leafs are attached to the lower end of the rod. When a charged object touches the metal knob at the outer end of the rod, the charge flow down throw the leaves. The leaves diverge (moves away) due to repulsion of the like charge. The degree of divergence of the leaves gives measure of the amount of charge.<\/p>\n\n\n\n
6.Method of charge<\/u><\/strong><\/p>\n\n\n\n (i) Charging by friction:-<\/u><\/em><\/strong><\/p>\n\n\n\n When a body having loosely bounded electrons, is rubbed with a body having strongly bounded electrons, then both the bodies becomes charged by transfer of e–<\/sup>.<\/p>\n\n\n\nE,g:- when glass rod is rubbed with fur then glass rod become +vely charged by transferring electron & fur become -vely charged by acquiring electron.<\/p>\n\n\n\n
\nBy loosing electron mass of the body decreases & by gaining e–<\/sup> mass of body increases. As electron have mass 9.1<\/u><\/em> 10-32<\/sup>kg.<\/u><\/em><\/li>\n<\/ul>\n\n\n\n (ii) Charging by electrostatic induction:-<\/u><\/em><\/strong><\/p>\n\n\n\n The phenomenon of charging a neutral body by placing it in the neighboring of a charge body is called electrostatic<\/em> induction.<\/p>\n\n\n\n\n\nWhen a positively charge body is bring toward a neutral body then charge separation takes place in neutral body which remains till the + vely charged body remains near to the neutral body. These induced charges may be explained in following ways.<\/p>\n\n\n\n
\nCharging by induction ( by earthing a conductor);-<\/strong>Suppose a neutral ball on an insulating stand & a positively charged glass rod is bringing toward it. Due to + ve charge on glass rod, the \u2013ve char<\/p>\n\n\n\n\n\n
\n Charging by induction ( By separating conductors)<\/strong> <\/p>\n\n\n\n
Q.1\u00a0 \u00a0how can you charge a metal sphere positively without touching it?<\/strong><\/p>\n\n\n\n\n<\/p>\n
Ans: By bringing a negatively charged body towared metal sphere.<\/p>\n
\n\n\n\n<\/p>\n
(iii)\u00a0 Charging by conduction (contact):-<\/u><\/strong><\/p>\n \n\n\n\n<\/p>\n
Charging by conduction requires the actual contact between the two bodies.<\/p>\n
\n\n\n\n<\/p>\n
In case of gold leaf electroscope when glass rod rubbed with silk is touched to the knob of leaf, than leaf diverse from their ac<\/p>\n
tu<\/p>\n
al position, which remains separated even after removal of glass rod. Thus charging may be done by conduction.<\/p>\n
\n\n\n\n\n\n<\/p>\n
7.\u00a0 Polar & Non Polar Bodies:-<\/u><\/strong><\/p>\n \n\n\n\n<\/p>\n
Polar body:- A body having different center of +ve& -ve charge is called polar body. E, g: – HCl , H2<\/sub>O etc.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/p>\n\n\n\n\n<\/p>\n
Non polar body:-A body having same center of +ve& -ve charge is called non polar body. \u00a0E, g: – H2<\/sub>, O2<\/sub>, N2<\/sub>, etc<\/p>\n\n\n\n\n<\/p>\n\n\n\n\n<\/p>\n
Q.2. (a) A comb run through one\u2019s dry hair attracts small bits of paper. Why? What happens if the hair is wet or if it is a rainy day? (Remember, a paper does not conduct electricity.)<\/strong><\/p>\n\n\n\n\n<\/p>\n
(b) Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. Why is this necessary?<\/strong><\/p>\n\n\n\n\n<\/p>\n
(c) Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. Why?<\/strong><\/p>\n\n\n\n\n<\/p>\n
\u00a0(d) A bird perches on a bare high power line, and nothing happens to the bird. A man standing on the ground touches the same line and gets a fatal shock. Why?<\/strong><\/p>\n\n\n\n\n<\/p>\n
Solution (a) this is because the comb gets charged by friction. The molecules in the paper gets polarized by the charged comb, resulting in a net force of attraction. If the hair is wet, or if it is rainy day, friction between hair and the comb reduces. The comb does not get charged and thus it will not attract small bits of paper.<\/p>\n
\n\n\n\n<\/p>\n
(b) To enable them to conduct charge (produced by friction) to the ground; as too much of static electricity accumulated may result in spark and result in fire.<\/p>\n
\n\n\n\n<\/p>\n
\u00a0(c) Reason similar to (b).<\/p>\n
\n\n\n\n<\/p>\n
(d) Current passes only when there is difference in potential.<\/p>\n
\n\n\n\n<\/p>\n
8.\u00a0 Some Basic Properties & electric charge:-<\/u><\/strong><\/p>\n \n\n\n\n<\/p>\n
Same as mass, charge is also a fundamental & intrinsic property of matter. As like charges repel each other & unlike charge attract each other. There are three basic properties of charge.<\/p>\n
\n\n\n\n<\/p>\n
(i) Quantization of charge (ii) conservative nature of charge (iii) Additive Nature of charge<\/p>\n
\n\n\n\n<\/p>\n
\n\nQuantization Of Charge:- (Discrete Nature of charge )<\/strong><\/li>\n\n<\/ul>\n\n\n\n\n<\/p>\n
According to quantization nature of charge, the charge on a body is always whole number multiple of charge on an electron.<\/p>\n
\n\n\n\n<\/p>\n
I,e charge on a body q = \u00a0ne\u00a0 \u00a0\u00a0n= 1, 2, 3, 4, \u2026\u2026\u2026 n\u2260 \u00bd, 3\/2, 1.5 etc.<\/p>\n
\n\n\n\n<\/p>\n
Where e = 1.6 10\u201319<\/sup>C (charge on an electron) & n is a whole number<\/p>\n\n\n\n\n<\/p>\n
\n\nDuring rubbing, electron can transfer from one body to another body in a whole number. So charge is quantized as half electron cannot be transferred.<\/em><\/li>\n\n\nA elementary particle quart of very small life time have fraction of charge.<\/em><\/li>\n\n<\/ul>\n\n\n\n\n<\/p>\n
\u00b1<\/em> e & \u00b1<\/em> \u00a0e. (it is exception of quantization of charge)<\/em><\/p>\n\n\n\n\n<\/p>\n
Q.3. \u00a0If 109<\/sup> electrons move out of a body to another body every second, how much time is required to get a total charge of 1 C on the other body?<\/strong><\/p>\n\n\n\n\n<\/p>\n
Solution:\u00a0 Therefore the charge given out in one second is= 1.6 \u00d7 10\u201319<\/sup> \u00d7 109<\/sup> C\u00a0\u00a0\u00a0\u00a0\u00a0 = 1.6 \u00d7 10\u201310<\/sup> C.<\/p>\n\n\n\n\n<\/p>\n
The time required to accumulate a charge of 1 C is<\/p>\n
\n\n\n\n<\/p>\n\n\n\n\n<\/p>\n
Thus to collect a charge of one coulomb, from a body from which 109<\/sup> electrons move out every second, we will need approximately 200 years.<\/p>\n\n\n\n\n<\/p>\n
\n\nOne coulomb is, therefore, a very large unit for many practical purposes.<\/li>\n\n<\/ul>\n\n\n\n\n<\/p>\n
\u00a0 Q.4. \u00a0how much positive and negative charge is there in a cup of water?<\/strong><\/p>\n\n\n\n\n<\/p>\n
Solution: \u00a0Let us assume that the mass of one cup of water is 250 g.<\/p>\n
\n\n\n\n<\/p>\n
The molecular mass of water is 18g. so we can say 18g of water contain 6.022×1023<\/sup> molecules \u00a0<\/p>\n\n\n\n\n<\/p>\n
\u00a0 \u00a0 \u00a0 1g of water contain
\n\n\n\n\n\n<\/p>\n
\u00a0<\/p>\n
\n\n\n\n<\/p>\n
Therefore the number of molecules in one cup of water is\u00a0
\n\n\n\n\n\n<\/p>\n
Each molecule of water contains two hydrogen atoms and one oxygen atom, i.e., 10 electrons and 10 protons.<\/p>\n
\n\n\n\n<\/p>\n
\u00a0Hence the total positive or total negative charge =<\/p>\n
\n\n\n\n<\/p>\n\n\n\n\n<\/p>\n
Q.5. A polythene piece rubbed with wool is found to have a negative charge of 3 \u00d7 10\u22127<\/sup> C. (a) Estimate the number of electrons transferred (from which to which?) (b) Is there a transfer of mass from wool to polythene?<\/strong><\/p>\n\n\n\n\n<\/p>\n
\n\nWhen polythene is rubbed against wool, electrons get transferred from wool to polythene. Hence, wool becomes positively charged and polythene becomes negatively charged. Amount of charge on the polythene piece, q = \u22123 \u00d7 10\u22127<\/sup> C<\/li>\n\n<\/ul>\n\n\n\n\n<\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Amount of charge on an electron, e = \u22121.6 \u00d7 10\u221219<\/sup> C<\/p>\n\n\n\n\n<\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Number of electrons transferred from wool to polythene = n<\/p>\n
\n\n\n\n<\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 as q = ne\u00a0 Therefore, the number of electrons transferred from wool to polythene is 1.87 \u00d7 1012<\/sup> .<\/p>\n\n\n\n\n<\/p>\n
(b) Yes. There is a transfer of mass taking place. This is because an electron has mass, me = 9.1 \u00d7 10\u22123<\/sup> kg Total mass transferred to polythene from wool, m = me<\/sub> \u00d7 n = 9.1 \u00d7 10\u221231<\/sup> \u00d7 1.85 \u00d7 1012<\/sup> = 1.706 \u00d7 10\u221218<\/sup> kg Hence, a negligible amount of mass is transferred from wool to polythene.<\/p>\n\n\n\n\n<\/p>\n
\n\nConservative nature of electric charge:-<\/u><\/em><\/strong><\/li>\n\n<\/ul>\n \n\n\n\n<\/p>\n
According to low of conservation of electric charge, the total charge on an isolated system remains constant, it can neither be created nor be destroyed& can only be transferred from one body to another body.E,g:- (i)<\/p>\n
\n\n\n\n<\/p>\n\n\n\n\n<\/p>\n
Here charge on reactant is zero & charge on product = +1-1=0<\/p>\n
\n\n\n\n<\/p>\n
So law of conservation of charge hold good.,<\/p>\n
\n\n\n\n<\/p>\n
(iii) Addition nature of electric charge:-<\/u><\/em><\/strong><\/p>\n \n\n\n\n<\/p>\n
According to additive nature of charge, the net charge on an isolated system can be simply obtained by adding all the charges scalarly.<\/p>\n
\n\n\n\n<\/p>\n
If a system having charge q1<\/sub>, q2<\/sub>, q3 <\/sub>\u2026qn <\/sub>then total charge on the system q = \u00a0q1<\/sub>+ q2<\/sub>+ q3 <\/sub>\u2026\u2026\u2026\u2026 qn<\/sub><\/p>\n\n\n\n\n<\/p>\n
E,g If system have four charges 2\u00b5C, 3\u00b5C, 4\u00b5C, -5\u00b5C<\/p>\n
\n\n\n\n<\/p>\n
Then total charge q = 2\u00b5C+ 3 \u00b5C+ 4 \u00b5C+( -5 \u00b5C)= 4 \u00b5C<\/p>\n
\n\n\n\n<\/p>\n
9. comparison of charge & mass :-<\/u><\/em><\/strong><\/p>\n \n\n\n\n<\/p>\n\n\n\n\n\u00a0<\/strong><\/td>\nElectric charge<\/strong><\/td>\nMass<\/strong><\/td>\n<\/tr>\n\n1<\/strong><\/td>\n\u00a0Electric charge may be + ve, -ve or zero.\u00a0\u00a0\u00a0<\/td>\n The mass of a body is always a positive.<\/td>\n<\/tr>\n \n2<\/strong><\/td>\nElectric charge is always quantized.<\/td>\n Quantization of mass is yet not obeyed.<\/td>\n<\/tr>\n \n3<\/strong><\/td>\nCharge on a body does not depend on its speed.\u00a0\u00a0<\/td>\n Mass of the body increase with its velocity.<\/td>\n<\/tr>\n \n4<\/strong><\/td>\nCharge is strictly conserved.<\/td>\n Mass is not conserved as it may convert into energy.<\/td>\n<\/tr>\n \n5<\/strong><\/td>\nThe electrostatic force between two charges may be attractive or repulsive.<\/td>\n Gravitational forces between two masses are always attractive.<\/td>\n<\/tr>\n \n6<\/strong><\/td>\nElectrostatic force between different charges may cancel out.<\/td>\n Gravitational forces between different masses never cancel out.<\/td>\n<\/tr>\n \n7<\/strong><\/td>\nA charged body always has some mass.<\/td>\n A body having mass may not have any charge.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n\n\n\n\n<\/p>\n
10. Coulombs law in electrostatics:- (Scalar form)<\/u><\/em><\/strong><\/p>\n \n\n\n\n<\/p>\n
In 1785, the French physicist Charles Augustan coulomb measured the electric force between small charged spheres by using a torsion balance & gave a law which is as below.<\/p>\n
\n\n\n\n<\/p>\n
Coulombs law states that the force of interaction between two stationary charge is directly proportion to the product of magnitude of charges & inversely proportional to the square of distance between the charges. This force acts along the line joining among the charges.<\/p>\n
\n\n\n\n<\/p>\n\n\n\n\n<\/p>\n
Where k is constant of proportionality & its value is<\/p>\n
\n\n\n\n<\/p>\n
\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0
\n\n\n\n\n\n<\/p>\n
Where
\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0
\n\n\n\n\n\n<\/p>\n
\u00a0<\/p>\n
\n\n\n\n\n\n<\/p>\n
So coulomb\u2019s law becomes<\/p>\n
\n\n\n\n<\/p>\n\n\n\n\n\n\n<\/p>\n
Unite of charge:-<\/u><\/strong><\/p>\n \n\n\n\n<\/p>\n
The S.I unite of electric charge is 1 coulomb.<\/p>\n
\n\n\n\n<\/p>\n
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