L3-circuits-I-2009 - Circuits, Currents, and Voltages Trac...

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1 Circuits, Currents, and Voltages Circuits, Currents, and Voltages Trac D. Tran ECE Department The Johns Hopkins University Baltimore, MD 21218 Outline Outline ± Electrical current and charge ± Water-model analogy ± Voltage ± Power and energy ± Kirchhoff’s current and voltage law ± Resistance ± Ohm’s Law ± Resistive circuit analysis
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2 Current and Charge Current and Charge ± Each electron carries an electrical charge of –1.602 x 10 coulombs ( C ) ± 1C = the charge of 6.242 x 10 electrons ± Variable: Q . Unit: coulomb ( C ) ± Current ² flow rate of electrical charge through a conductor or a circuit element ² Variable: I, i(t) ² Unit: ampere ( A ). 1A=1C/s ² Current-charge relationship –19 18 ) ( ) ( t q dt d t i = + = t t t q dt t i t q 0 ) ( ) ( ) ( 0 André-Marie Ampère (1775 – 1836) DC versus AC DC versus AC ± DC ² Direct current ² Current that is constant with time ² Abuse of notation: DC = constant ² For examples, I=3A or V=12V ± AC ² Alternating current ² Current that varies with time, for example, current that reverses its direction periodically (sinusoidal) ² Abuse of notation: AC = time-varying ² For examples, ( ) () t t v t t i π 200 cos 12 ) ( ; 2 cos 2 ) ( = = Nikola Tesla (1856 – 1943) Thomas Edison (1847 – 1931)
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3 Water Water -Model Analogy Model Analogy ± We cannot see electric current flowing in a wire ± Water-model or fluid-flow analogy helps us visualize the behaviors of electrical circuits and elements ± Current = flow of electrical charges flow of water molecules ± Assumptions ²
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This note was uploaded on 02/02/2010 for the course ENGINEERIN 520.101 taught by Professor Tracdtran during the Winter '06 term at Johns Hopkins.

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L3-circuits-I-2009 - Circuits, Currents, and Voltages Trac...

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