German University in Cairo Faculty of Information Engineering and Technology (IET) ELECTRIC CIRCUITS I (ELCT 301) LECTURE 1: BASIC CONCEPTS
COURSE INSTRUCTOR Instructor: Prof. Dr. Eng. Yasser G. Hegazy Vice President for Student Affairs Yasser.hegazy@guc.edu.eg Ph.D. (1996) Electrical and computer Engineering Department, University of Waterloo, Waterloo, Ontario, Canada. 31 years of university level teaching experience. Vice president for student affairs and dean of the faculty of EMS. 2
IMPORTANCE OF THE COURSE Electric circuits represent the foundation of electrical engineering studies and practices. All electrical systems can be modeled using the electric circuits approach. Learning how to build and analyze electric circuits constitute a milestone in building our engineering career. This course provide students with strong understanding of electric circuits with emphasis on the problem-solving skills and practical applications. 3
COURSE CONTENTS Introduction to Electric Circuits. (one week) Basic Laws of Electric Circuits. (3 Weeks) Techniques for Solving Electric Circuits. (5 weeks) Energy Storing Elements (one week) Transient response of First Order Circuits. (2 weeks) 4
STUDY PLAN Week Topic Assignments/ Quizzes Remarks I Introduction to Electric Circuits II Circuits Elements and Ohm s law Start of Tutorials and Labs III Kirchhoff's Laws & Voltage and Current Division Rules IV The Node-Voltage Method Assignment I & Quiz I V VI VII VIII IX X XI XII The Mesh-Current Method Superposition method/source Transformation Thevenin s and Norton s Circuits Midterm Exam No Lectures Maximum Power Transfer Theorem Inductors and Capacitors First Order Transients First Order Transients 5
STUDY RESOURCES Text Book Charles K. Alexander and Matthew Sadiku, Fundamentals of Electric Circuits Second Edition, McGrawHill, 2004. Reference Book. W. Nilsson and S. A. Riedel, Electric Circuits, Eights Edition or later. Upper Saddle River, NJ: Prentice Hall, 2011. Chapters 1 4 and 6,7. The rest will be covered in Circuits II. Webpage http://eee.guc.edu.eg/ 6
SCHEDULE OF CLASSES Lectures: Same lecture repeated at these time slots: - Mondays 3 rd in H14 and Monday 4 th in H13 (MECHATRONICS) Taught by Prof. Tarek Abdelsalam - Thursdays 1 st and 2 nd slots in H13. (IET/MET) Taught by Prof. Yasser Hegazy Tutorials : according to your schedule. Laboratories: according to your schedule. (The Electric Circuits labs are located in C3 second 209 and lab # 309) Instructor office hours: Every Sunday from 11:00 am to 1:00 p.m. in C7 office # 115 7
TUTORIALS Every week the instructor will assign problems from the text book. These problems will be posted on the course webpage In the tutorial, some of the assigned problems will be worked out on the board. You will be asked to hand in 3 assignments. Assignments grade will be based on the best 2. Three quizzes will be conducted to evaluate your performance and the quiz mark will be based on the best 2. 8
LABORATORIES Lab sessions are one slot/week. The lab manual is posted on the course webpage before your lab session. It is necessary to go through the lab manual before attending each lab session. The lab instructor will evaluate your performance during the lab and a lab report has to be submitted to your lab instructor at the end of each session. 9
MARKING SCHEME Activity % Quizzes (Best 2 of 3) 10 Tutorial Assignments 10 Laboratory Performance & Reports 15 Mid Term Examination 25 Final Total 40 100 10
INSTRUCTOR RECOMMENDATIONS FOR A SUCCESSFUL SEMESTER Try to attend all lectures, laboratories and tutorials for your own benefits and be on time. Make a good plan for your study and manage your time. Hand in the assignments, reports and quizzes on time, late reports will be penalized. Try to solve all the end of chapters problems to gain better problem solving skills. Update your instructor with any problem that might arise in the tutorial or in the lab. 11
LECTURE HALL RULES 12
CHAPTER 1: BASIC CONCEPTS 13
WHAT ARE ELECTRIC CIRCUITS? Electric circuits are models of electrical systems. Circuits are interconnection of electrical elements such as resistors, inductors, capacitors, and switches. Electrical circuit is a network that has a closed loop, giving a return path for the current. 14
SERIES AND PARALLEL CIRCUITS Series circuit One path for the electric current Failure of one bulb leads to breaking the circuit Parallel circuit Many paths for the electric Independent light bulbs and the circuit is not affected by the failure of one bulb.
WHAT ARE THE MAIN CIRCUIT ELEMENTS? There are active elements & passive elements Active elements can generate energy Voltage and current sources Batteries Passive elements cannot generate energy Resistors Capacitors and Inductors (but CAN store energy) V + I R capacitor 16
WHAT ARE THE MAIN CIRCUIT VARIABLES? Basic variables are, current (I), voltage (V) and power (P) Current: time rate of change of electric charge I = dq/dt A 1 Amp = 1 Coulomb/sec Voltage: electromotive force or potential, V =dw/dq 1 Volt = 1 Joule/Coulomb = 1 N m/coulomb Power: P = dw/dt = I V 1 Watt = 1 Volt Amp = 1 Joule/sec 17
VOLTAGE, V Voltage is the difference in energy level of a unit charge located at each of two points in a circuit, and therefore, represents the energy required to move the unit charge from one point to the other. Voltage Drop Circuit Element(s) + V(t) Voltage Rise 18
CURRENT, I Current is the flow of charge from a voltage source 1 Ampere ( Amp ) = Flow of 1 Coulomb/sec The sign of the current indicates the direction of flow. Types of current: direct current (dc): batteries and some special generators A B i + v alternating current (ac): household current which varies with time +++
PASSIVE SIGN CONVENTION When current enters the positive voltage terminal, the element is absorbing power (positive power). When current leaves the positive voltage terminal, the element is supplying V power (negative power). I + Circuit Element P = I V Positive (+) Power: element absorbs power Negative (-) Power: element supplies power i + _ + V In general: (Positive Power) + (Negative Power) = 0 20
EXAMPLE Calculate the power delivered or absorbed by each element in the shown circuit. Show that the sum of the delivered power = sum of the absorbed power. 21
SOLUTION 22
Good Luck 23