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Unformatted text preview: DC Circuits Basics Concepts and Laws 2 Basics Concepts and Laws Basic Concepts Charge and Current Voltage Power Passive Sign Convention Circuit Elements Ohm’s Law Kirchhoff’s Laws Series and parallel circuits Charge and Current 4 Charge 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 1019 C • Charge of a proton: q e = +1.602 x 1019 C 5 Charles Coulomb The unit of charge is the Coulomb (C) named after Colonel Charles Coulomb (17361806) a French engineer and physicist who published the laws of electrostatics in 178591. Coulomb’s Law describes the force between two charged particles. 6 Properties of Charge It is safe to treat charge as a continuous property in dealing with circuits. 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. 7 Current Current (i) is the rate at which charge is passing through an area: i = ∆ q/ ∆ t where i = the current in Amperes q = the charge in Coulombs t = the time in seconds ∆ = the change in a quantity 1 Ampere = 1 Coulomb/second 1 Ampere = 6,240,000,000,000,000,000 electrons per sec (6.24 x 10 18 ) 8 André Marie Ampère The unit of current is the Ampere (A) named after André Marie Ampère (17751836) a French mathematician, physicist and chemist who published the electrodynamic force law in 1826. 9 Direction of Current Flow Current is a signed quantity Physicists: Current flow in a conductor is due to electrons flowing from the negative terminal to the positive terminal of a voltage source. 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. 10 Current Flow – The Reality Current flow in a metallic conductor is due to electrons. Current flow in some other materials (plasmas, electrolytes) can be due to protons. It makes no difference as long as we are consistent. 11 Current Flow in Metallic Conductors Outer electrons are loosely bound to nucleus in metals Number electrons = number protons eee12 Current Flow in Metallic Conductors Electron moves to right. Effective positive charge moves to left. Net effect is electrons are flowing from negative to positive terminals. Same as positive “charge” flowing from positive to negative terminals. eee+ eee+ ee+ e13 Current is a Signed Quantity In electrical engineering, the positive direction of current flow is that of positive charges....
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 Spring '06
 MCCANN
 Volt, Windows 2000, Windows NT, Powe, RM plc

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