Notes on Chapter 26

# Notes on Chapter 26 - Chapter 26: Current and Resistance...

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24 June 2010 1 Chapter 26: Current and Resistance We consider charges in motion (electric current) in a conductor due to potential difference between the ends of the conductor. Examples of electric current are everywhere: Lightning Nerves currents control muscles Most electronic/electrical devices and power systems depend on current flow Flow of charges from the Sun important in telecommunications 26-1 What is Physics?

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24 June 2010 2 In this chapter we will introduce the following new concepts: Electric current ( symbol I or i ) Electric current density vector (symbol ) Drift speed (symbol v d ) Resistance (symbol R ) and resistivity (symbol ρ ) or conductivity (symbol σ ) of a conductor Ohmic and non-Ohmic conductors We will also cover the following topics: > Ohm’s law > Power in electric circuits J
24 June 2010 3 Pump Valve (A) Water Current (B) Electric Current Voltage Source

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24 June 2010 4 Electric current is the net transport of electric charge from one point to another across a section of the conductor. 26.2 Electric Current We consider steady electric current involving conduction electrons in metallic conductors when a battery is connected
24 June 2010 5 dq i dt = To find the total charge that passes through the plane we integrate over the time interval ( t 1 → t 2 ): 2 1 () t t q dq i t dt = = ∫∫ SI system of unit of electric current is called the ampere : 1 ampere = 1 A = 1 coulomb per second = 1 C/s Mathematical definition of current Rate of flow of charge through a cross-sectional area

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24 June 2010 6 Even though current is a scalar quantity , it is convenient to represent its direction with an arrow in circuit diagrams.
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## This note was uploaded on 09/30/2010 for the course PHYS MTH 203 taught by Professor None during the Spring '10 term at American University of Sharjah.

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Notes on Chapter 26 - Chapter 26: Current and Resistance...

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