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Lecture214Week10

# Lecture214Week10 - This Week Electric charge What is it...

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This Week Electric charge. What is it? Where is it? Voltage and energy What is a battery? Conductors and Insulators Bad idea to wave a golf club in a thunderstorm What is Lightning? Electrocution How does a microwave work? 12/09/11 Physics 214 Fall 2011 1

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12/09/11 Physics 214 Fall 2011 2 Electric charge an atom has a central nucleus of protons and neutrons surrounded by electrons Each element in the periodic table has a different combination of protons and neutrons. Hydrogen just has one proton and one electron. Electrons and protons carry electric charge and it is the force between the charges that hold the atom together. Charge comes in both negative (electrons) and positive (protons) and each carry one unit of charge . Normally objects have zero net charge but it is possible for an object to have charge which is a multiple of the unit charge either positive or negative. It is quite easy to separate electrons from atoms.
12/09/11 Physics 214 Fall 2011 3 Electromagnetism Almost every action in our everyday lives is due to the electromagnetic force caused by electric charges. Everything that is not due to gravity is electromagnetism. All transmission and use of electric power is due to the flow of electrons through wires. A camera flash is an example of separating positive and negative charge, which requires work. This work is then released as energy by letting the charges combine (lightning) If there is a separation of charge between two objects there will be a very strong attractive force which will transfer charge until the objects are neutral

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12/09/11 Physics 214 Fall 2011 4 Positive and negative Charge only occurs as a multiple of the unit charge on an electron or proton which is 1.6 x 10 -19 coulombs So any charge q is an integer multiple And N can be positive or negative q = N x 1.6 x 10 -19 coulombs Opposite charges attract Same sign charges repel
12/09/11 Physics 214 Fall 2011 5 Coulomb’s Law Coulomb’s Law F = kq 1 q 2 /r 2 (k = 9 x 10 9 N.m 2 /C 2 ) The force between two charges of one coulomb each separated by 1 meter is 9 x 10 9 Newtons (your weight ~ 1000N) The gravitational force between two 1 kg masses 1 meter apart is 6.67 x 10 -11 Newtons a difference of ~ 10 20 . F F r F ext F F Held in place To separate a negative charge from a positive charge requires work which is stored as potential energy. When the two charges are released this energy will be liberated as kinetic energy

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12/09/11 Physics 214 Fall 2011 6 Everyday charge In order to separate electrons from atoms requires work and frictional forces are sufficient to do this. Simple actions like rubbing two objects together or walking across a carpet will often result in a transfer of charge. This transfer is caused by stripping electrons
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Lecture214Week10 - This Week Electric charge What is it...

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