Ch 18 Electric Forces and Electric Fields

Ch 18 Electric Forces and Electric Fields - Lecture Notes...

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Electric Forces and Electric Fields Lecture Notes 18
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Goals ± To study electric charge, conductors, and insulators. ± To understand Coulomb’s law and solve some example problems. ± To understand electric fields. ± To calculate electrical forces. ± To map out electric field lines. ± To understand Gauss’ law and solve some example problems.
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Amber attracts bits of straw : ± Most of the world's amber is in the range of 30–90 million years old. ± Electrostatic charge can be generated by rubbing the amber with the fur of an animal e.g. a cat and has been done so while analyzing elementary charge for the first time. ± The modern term electron was coined in 1891 by the Irish physicist George Stoney, using the Greek word ' ηλεκτρον , meaning amber (and which was then translated as electr um ) because of its electrostatic properties and whilst analyzing elementary charge for the first time. The ending -on , common for all subatomic particles, was used in analogy to the word ion. An ant trapped in amber. Amber was much valued as an ornamental material in very early times Historical Notes
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Atomic charge arrangements Protons (+) and electrons (-) account for atomic charges. The Origin of Electricity ± The electrical nature of matter is inherent in atomic structure.
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Typical Examples: ± The SI unit for measuring the magnitude of an electric charge is the coulomb ( C ). ± The electron charge has been determined experimentally as: e = 1.60 × 10 19 C
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¾ In nature, atoms are normally found with equal numbers of protons and electrons, so they are electrically neutral . ¾ By adding or removing electrons from matter it will acquire a net electric charge with magnitude equal to e times the number of electrons added or removed, N . Ne q = Example 1 A Lot of Electrons How many electrons are there in one coulomb of negative charge? 18 19 - 10 25 . 6 C 10 1.60 C 00 . 1 × = × = = e q N
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The Electric Charge ± Electric charge (like mass) is an intrinsic property. ± The SI unit for measuring the magnitude of an electric charge is the coulomb (C). ± The electron charge has been determined experimentally as: e = 1.60 × 10 –19 C ± Electrons move, protons don’t. ± Electrons move/react in whole numbers.
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± When an ebonite rod is rubbed against animal fur, electrons from atoms of the fur are transferred to the rod . This transfer gives the rod a negative charge and leaves a positive charge on the fur. The body that loses electrons has an excess of positive charge , while the body that gains electrons has an excess of negative charge . ± It is possible to transfer electric charge from one object to another. Law of Conservation of Electric Charge During any process, the net electric charge of an isolated system remains constant (is conserved). ¾ Plastic, silk, rubber, glass and fur can reveal fundamental behaviors of charge.
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This note was uploaded on 04/01/2011 for the course PHY 135 taught by Professor Wagihghobriel during the Spring '11 term at University of Toronto- Toronto.

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Ch 18 Electric Forces and Electric Fields - Lecture Notes...

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