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241-25_Lec-10 (1) - Physics 241 Lecture 10 Y E Kim Chapter...

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Physics 241 Lecture 10 Y. E. Kim September 23, 2010 Chapter 25, Sections 1 - 5 September 23, 2010 University Physics, Chapter 25 1
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September 23, 2010 University Physics, Chapter 25 2 Direct Current We will study charges in motion Electric charge moving coherently from one region to another is called electric current Current is flowing through light bulbs, iPods, and lightning strikes Current usually consists of mobile electrons traveling in conducting materials Direct current is defined as a current that flows only in one direction in the conductor Most of our electric technology is based on Alternating Current Chapter 26 Computers, electronic devices are based on direct currents.
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September 23, 2010 University Physics, Chapter 25 3 Electric Current (1) We define the electric current i as the net charge passing a given point in a given time Random motion of electrons in conductors, or the flows of electrically neutral atoms, are not electric currents in spite of the fact that large amounts of charge are moving past a given point If net charge dq passes a point in time dt we define the current i to be dq i dt
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September 23, 2010 University Physics, Chapter 25 4 Electric Current (2) The amount of charge q passing a given point in time t is the integral of the current with respect to time given by Charge conservation implies that charge flowing in a conductor is never lost Therefore the same amount of charge must flow into one end of the conductor and exit from the other end of the conductor 0 t q dq idt
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