chapter15.1-15.3_lecture

chapter15.1-15.3_lecture - Electric Forces and Electric...

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Unformatted text preview: Electric Forces and Electric Fields ` Charge is an intrinsic property of matter (particles) ` Two types of charges exist ◦ They are called positive and negative ◦ Named by Benjamin Franklin ` Like charges repel; unlike charges attract ` Demo (ping-pong ball) +- + + +- ` Charge is quantized: all charge is a multiple of a fundamental unit of charge, symbolized by e ◦ Quarks are the exception ◦ The SI unit of charge is the Coulomb (C) ` Nature’s basic carrier of positive charge is the proton; nature’s basic carrier of negative charge is the electron ` Atoms are normally neutral, i.e., consist of equal amount of positive and negative changes ` If an electron is knocked out, what is left will be positively charged. ` In most cases, objects becomes charged because negative charges (i.e., electrons) are transferred from one object to another An atom Why most matter appear uncharged? How does an object get charged? Don’t get confused with this conductor. ` Conductors are materials in which the electric charges move freely in response to an electric force ◦ Copper, aluminum and silver are good conductors ◦ Some water solutions are also good conductors x Stay away from water near downed electric lines! ◦ When a conductor is charged in a small region, the charge readily distributes itself over the entire surface of the material ◦ All electric wires are made of good conductors ` Insulators are materials in which electric charges do not move freely ◦ Glass and rubber are examples of insulators ◦ Other examples: dry wood, most ceramics, plastics ◦ When insulators are charged (e.g., by rubbing), only the rubbed area becomes charged ◦ There is no tendency for the charge to move into other regions of the material – charges are “stuck” Electrical cable conductor insulator ` The characteristics of semiconductors are between...
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chapter15.1-15.3_lecture - Electric Forces and Electric...

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