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Unit 1.3 Physical Basics_edited

Unit 1.3 Physical Basics_edited - Physical Basics In this...

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1 1 Unit 1: Basic Circuit Theory Unit 1.3: Physical Basics 2 Physical Basics f In this lecture, you will learn about: Charge Current and Voltage Energy and Power Ideal basic circuit element Passive sign convention f These fundamental concepts will provide the foundation for everything you will learn in this course 3 Charge, Current and Voltage 4 Charge f CHARGE is the fundamental electric quantity All electrical phenomena are caused by charge— both to the separation of charge or charges in motion f Charge of an electron: q e = -1.602 x 10 -19 C f Charge of a proton: - q e = +1.602 x 10 -19 C f Obviously, q e is very small when measured in Coulombs. f It takes many, many electrons to produce a meaningful amount of electric current. 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 More Properties of Charge f It is safe to treat charge as a continuous property in dealing with circuits—Law of Large Numbers 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. f 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.
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2 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 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 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 nomenclature that current is due to positive charges flowing from the positive terminal to the negative terminal of a voltage source 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 Truth 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 The truth: it makes no difference as long as you 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 -
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3 13 Current Flow in Metallic Conductors f Electron moves to right.
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