01(T)%20-%20Electric%20Charge%20and%20Electric%20Field

01(T)%20-%20Electric%20Charge%20and%20Electric%20Field - 1...

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1 - ELECTRIC CHARGE AND ELECTRIC FIELD Page 1 1.1 Electric Charge Of almost more than 100 fundamental particles of matter, three most important are electron, proton and neutron. Their masses are m e = 9.1 × 10 - 31 kg, m p 2245 m n = 1.6 × 10 - 27 kg respectively. Gravitational force of attraction between two electrons 1 cm apart is 5.5 × 10 - 67 N, whereas electrical force of repulsion due to electric charge on them is 2.3 × 10 - 24 N which is much stronger. Electric charge can be positive or negative. Traditionally, charge of proton is considered positive and that of electron negative although reverse sign convention would have made no difference. Like charges repel each other and unlike charges attract. Electroscope is used to detect charges. Electrons revolving around the nucleus are weakly bound as compared to the force with which protons are bound inside the nucleus. Hence, during exchange of electrons between two bodies, electrons get transferred from one body to the other. S Ι ΙΙ unit of charge is coulomb denoted by C. It is the charge passing in 1 second through any cross-section of a conductor carrying 1 ampere current. Magnitude of charge on an electron or a proton is 1.6 × 10 - 19 C. Electric charge, like mass, is a fundamental property which is difficult to define. 1.2 Quantization of Electric Charge The magnitudes of all charges found in nature are in integral multiple of a fundamental charge ( Q = ne ). This fact is known as the quantization of charges. This fundamental charge is the charge of an electron and is denoted by e. All fundamental charged particles possess charge having magnitude e. For example, a proton and a positron ( positive electron ) possess positive charge ( +e ). Atom as a whole is electrically neutral as there are equal number of protons and electrons in it. This fact has been verified with an accuracy of 1 in 10 20 . No theory has been able to satisfactorily explain the quantization of charges so far. Protons and neutrons are believed to be made up of more fundamental particles called quarks. Quarks are of two types; ‘up quark’ possessing +( 2 / 3 )e charge and ‘down quark’ possessing -( 1 / 3 )e charge. The independent existence of quarks is not detected so far. 1.3 Conservation of Electric Charge Irrespective of any process taking place, the algebraic sum of electric charges in an electrically isolated system always remains constant. This statement is called the law of conservation of charge. In an electrically isolated system, a charge can neither enter nor leave it. Any charge-less matter or radiation can enter or leave the system. γ - ray photon entering the system may
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1 - ELECTRIC CHARGE AND ELECTRIC FIELD Page 2 produce an electron-positron pair which as a whole being electrically neutral does not alter the original charge of the system. 1.4
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This note was uploaded on 11/28/2011 for the course PHYSICS 300 taught by Professor Smith during the Spring '06 term at ITT Tech Flint.

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01(T)%20-%20Electric%20Charge%20and%20Electric%20Field - 1...

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