FUNDAMENTALS OF ELECTRIC CIRCUITS EE 318 Dr. ARVIND TIWARI B1-S DEPARTMENT OF ELECTRICAL ENGINEERING, COLLEGE OF ENGINEERING AL-QASSIM UNIVERSITY 1

AssessmentAssessment task (test, group project, examination etc.)Week dueWeight of 1Quiz 1Week 22% 2Assignment 1Week 42% 3Quiz 2Week 42% 4Quiz 3Week 52% 55Mid Term Exam1Week 615% 6Quiz 4Week 82% 7Quiz 5Week 92% 8Mid Term Exam2Week 1215% 9Assignment 2Week 132% 10Continuous class evaluation1 st -15 th 2% 11Attendance1 st -15 th 4% 12Final ExamWeek 1650% SCHEDULE OF ASSESSMENT 2

CIRCUIT ELEMENTS RESISTOR, CURRENT,VOLTAGE, POWER, ENERGY, OHM’S Law FUNDAMENTALS OF ELECTRIC CIRCUITS 3

Circuit Elements 5 ideal basic circuit elements: –voltage source –current source –resistor –inductor –capacitor Many practical systems can be modeled with just sources and resistors The basic analytical techniques for solving circuits with inductors and capacitors are the same as those for resistive circuits active elements, capable of generating electric energy passive elements, incapable of generating electric energy 4

ATOMS AND THEIR STRUCTURE The orbiting electron carries a negative charge equal in magnitude to the positive charge of the proton In all other elements, the nucleus also contains neutrons, which are slightly heavier than protons and have no electrical charge. 5

The atomic structure of any stable atom has an equal number of electrons and protons. Different atoms have various numbers of electrons in concentric orbits called shells around the nucleus. The number of electrons in each succeeding shell is determined by 2n 2 where n is the shell number. The atomic structure of copper Total number of electrons = 32 Last shell electron = 1 Is farthest from the nucleus The force of attraction between the nucleus and the 29th electron of copper can be determined by Coulomb’s law 6

VOLTAGE Every source of voltage is established by simply creating a separation of positive and negative charges If we separate the 29th electron from the rest of the atomic structure of copper,we create regions that have a net positive and negative charge. For the region inside the dashed boundary, the number of protons in the nucleus exceeds the number of orbiting electrons by 1, so the net charge is positive. This positive region created by separating the free electron from the basic atomic structure is called a POSITIVE ION If 29th electron gains sufficient energy from the surrounding medium to leave the parent atom, it is called a free electron COULOMB’S LAW 7

If the free electron then leaves the vicinity of the parent atom, regions of positive and negative charge have been established. This separation of charge to establish regions of positive and negative charge is the action that occurs in every battery. Through chemical action, a heavy concentration of positive charge (positive ions) is established at the positive terminal, with an equally heavy concentration of negative charge (electrons) at the negative terminal. One coulomb of charge is the total charge associated with 6.242X10 18 electrons If we take a coulomb of negative charge near the surface of the positive charge and move it toward the negative charge, energy must be expended to overcome the repulsive forces of the larger negative charge and the attractive forces of the positive charge 8

Q. Find the voltage between two points if 60 J of energy are required to move a charge of 20 C between the two points. if a total of 1 joule (J) of energy is used to move the negative charge of 1 coulomb (C), there is a difference of 1 volt (V) between the two points. VOLTAGE 9

CURRENT The applied voltage is the starting mechanism—the current is a reaction to the applied voltage In the conducting wire, the free electrons generated at room temperature are in constant motion in random directions. At any instant of time, the number of electrons crossing the imaginary plane in one direction is exactly equal to that crossing in the opposite direction, so the net flow in any one direction is zero. To make this electron flow do work, we need to give it a direction and be able to control its magnitude. This is done by applying a voltage across the wire to force the electrons to move toward the positive terminal of the battery 10

The current in amperes is given by The applied voltage (or potential difference) in an electrical/electronics system is the “pressure” to set the system in motion, and the current is the reaction to that pressure. VOLTAGE SOURCES An electromotive force (emf) is a force that establishes the flow of charge (or current) in a system due to the application of a difference in potential. DC voltage sources can be divided into three basic types: (1)batteries (chemical action or solar energy), (2)generators (electromechanical), (3)power supplies if 6.242x10 18 electrons (1 coulomb) pass through the imaginary plane in 1 second, the flow of charge, or current, is said to be 1 ampere (A). 11

CONDUCTORS, SEMICONDUCTORS AND INSULATORS Conductors are those materials that permit a generous flow of electrons with very little external force (voltage) applied. Good conductors typically have only one electron in the valence (most distant from the nucleus) ring. Insulators are those materials that have very few free electrons and require a large applied potential (voltage) to establish a measurable current level. Semiconductors are a specific group of elements that exhibit characteristics between those of insulators and those of conductors. Semiconductor materials typically have four electrons in the outermost valence ring. 12

The opposition to the flow of charge through an electrical circuit, called resistance, it has the units of ohms and uses the Greek letter omega ( Ω ) as its symbol. This opposition, due primarily to collisions and friction between the free electrons and other electrons, ions, and atoms in the path of motion, converts the supplied electrical energy into heat that raises the temperature of the electrical component and surrounding medium. RESISTANCE: CIRCULAR WIRES The resistance of any material is due primarily to four factors: 1. Material 2. Length 3. Cross-sectional area 4. Temperature of the material The first three elements are related by the following basic equation for resistance The material is identified by a factor called the resistivity, which uses the Greek letter rho (r) as its symbol and is measured in CM-/ft. 13

The higher the resistivity, the greater the resistance of a conductor. The longer the conductor, the greater the resistance The greater the area of a conductor, the less the resistance What is the resistance of a 100 ft length of copper wire with a diameter of in. at 20°C? 14

RESISTANCE: METRIC UNITS In SI units, the resistivity would be measured in ohm-meters, the area in square meters, and the length in meters. However, the meter is generally too large a unit of measure for most applications, and so the centimeter is usually employed. 15

TEMPERATURE EFFECTS Conductors An increase in temperature results in an increase in the resistance level. Consequently, conductors have a positive temperature coefficient. SemiconductorsAn increase in temperature results in a decrease in the resistance level. Consequently, semiconductors have negative temperature coefficients. 16

Insulators An increase in temperature results in a decrease in the resistance of an insulator. The result is a negative temperature coefficient. Temperature Coefficient of Resistance The higher the temperature coefficient of resistance for a material, the more sensitive the resistance level to changes in temperature. 17

TYPES OF RESISTORS Fixed Resistors For a particular style and manufacturer, the size of a resistor increases with the power or wattage rating The size of a resistor does not define its resistance level. 18

Variable ResistorsThe resistance between the wiper arm and either outside terminal can be varied from a minimum of 0 to a maximum value equal to the full rated value of the potentiometer. 19

CONDUCTANCEThe reciprocal of the resistance of a material, we have a measure of how well the material conducts electricity. The quantity is called conductance, has the symbol G, and is measured in siemens (S) OHM’S LAW Every conversion of energy from one form to another can be related to this equation. In electric circuits, the effect we are trying to establish is the flow of charge, or current. The potential difference, or voltage, between two points is the cause (“pressure”), and the opposition is the resistance encountered. 20

The symbol E is applied to all sources of voltage The symbol V is applied to all voltage drops across components of the network Both are measured in volts and can be applied interchangeably For any resistor, in any network, the direction of current through a resistor will define the polarity of the voltage drop across the resistor 21

22

PLOTTING OHM’S LAW 23

24

POWER It provides an indication of how much work (energy conversion) can be accomplished in a specified amount of time; that is, power is a rate of doing work. The power associated with any supply is not simply a function of the supply voltage. It is determined by the product of the supply voltage and its maximum current rating. 25

ENERGY The energy (W) lost or gained by any system is therefore determined by Since power is measured in watts (or joules per second) and time in seconds, the unit of energy is the watt- second or joule 26