EE302-2H-Circuit Basics-3pp

# EE302-2H-Circuit Basics-3pp - EE302 2.1 Physical Basics DC...

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8/29/2007 Dr. Bruce McCann 1 EE302: 2.1 - Physical Basics DC Circuits Basics Concepts and Laws 2 Basics Concepts and Laws f Basic Concepts ± Charge and Current ± Voltage ± Power ± Passive Sign Convention f Circuit Elements f Ohm’s Law f Kirchhoff’s Laws f Series and parallel circuits Charge and Current

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8/29/2007 Dr. Bruce McCann 2 EE302: 2.1 - Physical Basics 4 Charge f The fundamental electric quantity ± All electrical phenomena are caused by charge • Separation of charge or • Motion of charge ± Unit: Coulomb (C) • Charge of an electron: q e = -1.602 x 10 -19 C • Charge of a proton: - q e = +1.602 x 10 -19 C 5 Charles Coulomb f The unit of charge is the Coulomb (C) named after Colonel Charles Coulomb (1736-1806) a French engineer and physicist who published the laws of electrostatics in 1785-91. f Coulomb’s Law describes the force between two charged particles. 6 Properties of Charge f It is safe to treat charge as a continuous property in dealing with circuits. f Charge is conserved. ± Charge may be transferred from one part of a circuit to another, but the total amount of charge does not change. ± This is a result of conservation of matter. • Charge is due to electrons and protons. • Electrons and protons are neither created nor destroyed in an electric circuit.
8/29/2007 Dr. Bruce McCann 3 EE302: 2.1 - Physical Basics 7 Current f Current (i) is the rate at which charge is passing through an area: i = Δ q/ Δ t where i = the current in Amperes q = the charge in Coulombs t = the time in seconds Δ = the change in a quantity f 1 Ampere = 1 Coulomb/second f 1 Ampere = 6,240,000,000,000,000,000 electrons per sec (6.24 x 10 18 ) 8 André Marie Ampère f The unit of current is the Ampere (A) named after André Marie Ampère (1775-1836) a French mathematician, physicist and chemist who published the electrodynamic force law in 1826. 9 Direction of Current Flow f Current is a signed quantity f Physicists: ± Current flow in a conductor is due to electrons flowing from the negative terminal to the positive terminal of a voltage source. f Electrical Engineers: ± Use the convention that current is due to positive charges flowing from the positive terminal to the negative terminal of a voltage source.

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8/29/2007 Dr. Bruce McCann 4 EE302: 2.1 - Physical Basics 10 Current Flow f You can blame the confusion on Ben Franklin. ± “Positive” was a surplus of electrical “fluid”. ± “Negative” was a lack of electrical “fluid”. ± The fluid flowed from positive to negative. 11 Current Flow – The Reality f Current flow in a metallic conductor is due to electrons. f Current flow in some other materials (plasmas, electrolytes) can be due to protons. f It makes no difference as long as we are consistent. 12 Current Flow in Metallic Conductors f Outer electrons are loosely bound to nucleus in metals f Number electrons = number protons e - e - e -
8/29/2007 Dr. Bruce McCann 5 EE302: 2.1 - Physical Basics 13 Current Flow in Metallic Conductors f Electron moves to right.

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## This note was uploaded on 02/26/2012 for the course ECE 302 taught by Professor Preston during the Spring '08 term at University of Texas.

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EE302-2H-Circuit Basics-3pp - EE302 2.1 Physical Basics DC...

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