241-21_lec-2

# 241-21_lec-2 - Physics 241 Lecture 2 Y E Kim University...

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Physics 241 Lecture 2 Y. E. Kim August 26, 2010 August 30, 2010 University Physics, Chapter 21 1

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Quiz Are you here ? a) Yes b) No
August 30, 2010 University Physics, Chapter 21 3 Summary from the previous lecture There are two kinds of electric charge positive and negative. Law of Charges Like charges repel and opposite charges attract The unit of charge is the coulomb defined as 1 C = 1 A•s Law of charge conservation The total charge of an isolated system is strictly conserved.

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August 30, 2010 University Physics, Chapter 21 4 Electrostatic Charging There are two ways to charge an object Conduction Induction Charging by conduction We can charge an object by connecting a source of charge directly to the object and then disconnecting the source of charge The object will remain charged Conservation of charge
August 30, 2010 University Physics, Chapter 21 5 Charging by Conduction We brought charge onto the electroscope through contact with the electrode. Electroscope + + + + + + + + + + + + + + + + + +

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August 30, 2010 University Physics, Chapter 21 6 Induction The presence of the positively charged rod leads to a redistribution of charge (a kind of polarization). It pulls electrons up to the electrode . - - - - - - - - - + + + + + + + + + + + + + + + + + +
August 30, 2010 University Physics, Chapter 21 7 Charging by Induction We can also charge an object without physically connecting to it First we charge a rod positively Then we ground the object to be charged Connecting the object to the Earth provides an effectively infinite sink for charge We bring the charged rod close to the object but do not touch it We remove the ground connection and move the rod away The object will be charged by induction

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August 30, 2010 University Physics, Chapter 21 8 The presence of the positively charged rod leads to a redistribution of charge. Grounding pushes positive charge to Earth (or rather pulls electrons from Earth!) leaving the electroscope negative.
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## This note was uploaded on 07/15/2011 for the course PHYS 241 taught by Professor Wei during the Summer '08 term at Purdue.

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241-21_lec-2 - Physics 241 Lecture 2 Y E Kim University...

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