EECS
2015+1-1,2,3+all.pdf

# Typical problems for self assessment 15 conquest

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Typical problems for self-assessment 15 ConQuest = Conceptual questions 16 Summary 17 Book Page 2

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EE for the 21 st century Review the basics 1-1-1 Kirchhoff’s law for electric currents © 2015 Alexander Ganago Page 2 of 17 Last printed 2015-07-24 6:15 PM File: 2015 1-1-1 KCL.docx B ASIC FACTS ABOUT ELECTRIC CHARGES , CURRENTS , AND CIRCUITS All material objects in this world are built of moving, charged particles, which form atoms, molecules, and crystals. The human body also includes moving electric charges, to be discussed in more detain in the Unit on electrical safety. <Sidebar> All material objects in this world are built of moving, charged particles. There are two types of charges, called positive (such as protons in the nuclei) and negative (such as electrons surrounding the nuclei). <Sidebar> There are two types of charges, called positive and negative. Notably, the magnitude of an elementary positive charge (that of a proton) exactly equals the magnitude of an elementary negative charge (of an electron). Thus usual materials are electrically neutral: the sum total of all positive charges plus all negative charges is exactly zero. <Sidebar> The magnitude of an elementary positive charge (of a proton) exactly equals the magnitude of an elementary negative charge (of an electron). Usual materials are electrically neutral: the sum total of all positive charges plus all negative charges is exactly zero. The fundamental principle of conservation of electric charge in our Universe maintains that the algebraic sum of positive and negative electric charges remains constant in any closed system. <Sidebar> The fundamental principle of conservation of electric charge maintains that the algebraic sum of positive and negative electric charges remains constant in any closed system. Thus, positive and negative charges can be ü Separated, for example: o When an electron breaks its bond with an atom or molecule and moves away, leaving behind a positively charged ion, or o When a very high-energy cosmic ray produces a pair of electron and positron, carrying opposite charges of the same magnitude ü Recombined, for example: o When an electron rejoins a positive ion, forming a neutral atom or molecule, or o When an electron and a positron annihilate, producing a high-energy quantum of radiation. Both positive and negative charges are moved by electric fields. Motion of charges creates the electric current, which is defined as the amount of charge that passes through the cross-section of a conductor per unit time. <Sidebar> Electric current is defined as the amount of charge that passes Book Page 3
EE for the 21 st century Review the basics 1-1-1 Kirchhoff’s law for electric currents © 2015 Alexander Ganago Page 3 of 17 Last printed 2015-07-24 6:15 PM File: 2015 1-1-1 KCL.docx through the cross-section of a conductor per unit time.

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• Fall '07
• Ganago
• Electric charge, Alexander Ganago

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