Module 1_3: DC/AC Sources and Electrical Circuit Components PDF

Chapter I. DC/AC Sources and Electrical Circuit Components, Voltage and Current Laws I. Electron Theory A. Atoms All matter whether a gas, liquid, or solid is composed of atoms. Atoms are made of fundamental substomic particles called pro...

Chapter I. DC/AC Sources and Electrical Circuit Components, Voltage and Current Laws I. Electron Theory A. Atoms All matter whether a gas, liquid, or solid is composed of atoms. Atoms are made of fundamental substomic particles called protons, neutrons, and electrons. PROTON - positively charged particles that are inside the nucleus of an atom. ELECTRON - negative charge that is found in all atoms. NEUTRON - neutral sub-atomic particles. Microscopic Solar System B. Orbital Electrons All negatively charge electrons revolve about the positive nucleus (protons plus neutrons) in definite orbits that depend upon certain energy relationship. In atomic theory and quantum mechanics, an atomic orbital is a function describing the location and wave-like behavior of an electron in an atom. There are three kinds of energy possesses as the electron revolves,  the energy required to displace the electron from nucleus that it may revolve at some fixed radius from the atomic center,  the energy represented by its motion around the nucleus, and  the energy that results from its spin on its own axis. C. Valence Electrons and Conductivity in Solids Atoms can combine in orderly and repetitive arrangement to form the kinds of solid used in electrical circuit, also called as electric conductor. Three common electric conductors are silver, copper, and aluminum. These three conductors have typical crystal structure. It is cubic structure of metallic molecule. The particular geometric pattern of the crystal, the crystal lattice, is maintained by the bonding of the electrons in the outer shell which called valence electrons. They are in conductors generally free to move from atom to atom. This electron mobility that is responsible for the conduction process.  In Electrical Conductivity, solid materials may be classified as conductor, insulators, and semiconductors. Good conductors- fewer than four valence electrons (ex. copper has 1, and aluminum has 3) Poor conductors-have more than four valence electrons (ex. phosphorus has 5), also called as insulator Semiconductor- exactly have 4 valence electrons (ex. germanium has 4)  Copper, silver, and aluminum are excellent conductors because they have enormous number of free electrons. Elements No. of Free Electrons/IN3 Copper 1.64 x 1024 Silver 1.68 x 1024 Aluminum 1.0 x 1024 In contrats, rubber extremely poor conductor because has about 3 free electrons per cubic inch only. II. Electric Charge and Electric Current Electric current is, in fact, represented by a transfer of electric charge. The application of of an electric pressure to a conductor imparts lateral motion to its free electrons because the latter are charged. The magnitude of the charge is commonly given in coulombs.  each negatively charge electron = 1.56 x 10-19 Coulomb  concentration of 6.28 x 1018 electrons=1 Coulomb When one coulomb of electric charge continously passes a given point every second the electric current is said to be one ampere. 𝑸 where I = current, Amp 𝑰 = Q = charge, Coulombs 𝒕 t = time, Sec, during electrons move  The quantity Q (coulomb) is, geometrically the area, if I (ampere) is plotted along one axis, the ordinate and t (second) is plotted along perpendicular axis, the abscissa. Relation between Current and Time I(A) Q=It Quiz No. 1: 0 t (sec ) The current in a conductor changes uniformly from 0 to 3 amp in 3 sec, remains steady at 3 amp for 5 sec, and then drops uniformly to 1.5 amp in 7 sec. Calculate the total amount of charge transferred in the elapsed time of 15 secs. Sample Problem 1. Calculate the number of free electrons in a copper conductor having a diameter of 0.064 inches and a length of 1000 ft. no of free electrons = = = 6.33 x 1025 electrons 2. Find the current in amperes if 1000 Coulombs pass through a wire or a conductor in 2 minutes. 2 min = 120 sec I= = = 8.33 A 3. Given current variation in a given conductor. Determine (a) Q total charge; (b) I ave Quiz No. 2 Will a fuse rated at 4 amperes blow if 200 C pass through with it in 1.2 minutes? III. Electron Velocity in Conductors For Copper Let u be the electron velocity, in/sec u= 1. Given A=0.00161 in2, I=4.5 A. Determine electron velocity of (a) copper, (b) aluminum. Quiz no. 3 Determine the number of trips of the load current on the copper wire in 24 hours IV. EMF (Electromotive Force) or VOLTAGE -the characteristic of a device or machine that tends to create electron flow. Example battery, generator etc. V. Electrical Resistance and Resistivity Resistivity Is a specific resistance or constant that depends on the characteristic or conductivity of materials Material ρ (Ω m) at 20 °C L R  , ohms() Resistivity A Silver 1.59×10−8 Annealed copper 1.72×10−8 Aluminum 2.82×10−8  Volume Resistivity 1. The resistance of a conductor varies directly as the square of the length when the volume is fixed. L R= L2 R  V 2.The resistance of a conductor varies inversely as the square of its cross section when the volume is fixed. Sample Problem 1. Calculate the resistance of 3500 feet copper wire having a diameter 0.5 in with resistivity equal 1.724μΩ - cm. 2. Determine the resistance of a bus bar made of copper if the length is 10 meters long and the cross-section is a 4x4 cm2. VI. Kinds of Current 1.Unidirectional Direct Current When the current does vary somewhat in magnitude but does not reverse in direction. 2. Direct Current Is one in which energy takes place unidirectionally or it is a steady flow of electric charge in one direction around the loop. 3.Pulsating Direct Current Is one in which the magnitude varies considerably and pulsated regularly there being no change in direction. 4. Alternating Current Current changes periodically in magitude as well as direction. 5. Oscillating Current Alternating in character, increases and decreases in magnitude and changes in direction periodically with respect to time. VII. Kinds of Voltage Emfs, i.e., voltages are, for the most part, quite similar to currents with regard to changes in magnitude and direction. These are therefore referred to by such terms as Direct Currect-DC Voltage or Alternating Current-AC voltage or oscillating emf.