# E E 2440 Circuits I - Introduction E E 1205 Circuit Analysis Lecture 1 - Introduction to Electrical Engineering Overview of Electrical Engineering Electrical engineers design systems with two main objectives: to Gather, store, process, transport or present information Distribute, and convert energy between different forms Electrical systems can be

divided into seven major classifications. 7 Linked Classifications of Electrical Systems Communications Systems Computer Systems Control Systems Electromagnetics Electronics

Power Systems Signal Processing Systems Communications Systems Telephony Analog and Digital Switched Channels Radio Broadcast AM, FM, & SW Two-Way Television Computer Systems Programmable Microcircuits

High-speed switching of logic circuits Used for Computation Control Control Systems Automated Adaptable Faster Operation than Manual More Reliable than Manual Modern high-performance aircraft rely on automated control systems Electromagnetics Antennas for Sending & Receiving

Information Cell Phones Satellite Dishes Magnetrons for generation of Microwave Energy Induction Heating for Industrial processes Electronics Material Properties Devices Circuits

Used for Detecting, Amplifying and Switching Electrical Signals Power Systems Large networks connected by low frequency a-c transmission lines Small networks in aircraft and spacecraft Electromechanical Energy Conversion Power Electronics High frequency switching converters High efficiency, high power density Signal Processing Systems Transform and manipulate

signals and the information they contain Image processing Data from weather satellites MRI scans of the human body Noise reduction Encryption Circuit Theory Mathematical modeling of physical phenomena Circuit theory is a special case of electromagnetic field theory General EM theory is more complex than circuit theory

General EM theory requires more complex mathematics Three Basic Assumptions of Circuit Theory Electric effects happen instantaneously throughout a system Net Charge on every component in the system is zero No magnetic coupling between components c f Effect of Frequency Frequency

Wavelength Usage 0 Hz (DC) Infinite Basic Power 60 Hz 5000 km Power 400 Hz

750 km Aircraft Power 1000 Hz 300 km Acoustic 1000 kHz 300 m AM Radio 500 MHz

60 cm Television 2.45 GHz 122.4 mm Microwave Oven 20 GHz 15 mm K-band Radar

Problem Solving Identify what is given and what is to be found. Sketch a circuit diagram or other visual model Think of several solution methods and a way of choosing between them Calculate a solution Problem Solving (continued) Use your creativity If your efforts are not converging to a solution, you may want to rethink your assumptions.

Force newton (N) kgm/s2 Energy or work joule (J) Nm Power watt (W) J/s Electric charge coulomb As Electric potential volt (V) W/A Electric resistance ohm () V/A Electric conductance siemens (S)A/V International System of Units (continued) Electric capacitance

farad (F)C/V Magnetic flux weber (Wb)Vs Inductance henry (H) Wb/A Standardized Prefixes atto a femto

pico p nanon micro milli m centic deci d 10-18 f 10-15 10-12 10-9 10-6 10-3 10-2 10-1

deka da10 hecto h 102 kilo k 103 mega M 106 giga G 109 tera T 1012 peta P 1015 exa E 1018 Circuit Analysis: An

Overview A circuit model is used to connect our visualization to our analysis of a physical system The elements of our circuit model are ideal circuit components. The behavior of output parameters is governed by physical/mathematical laws for the elements of the circuit model. Voltage and Current Voltage is the energy per unit of charge. dw

v dq Current is the rate of flow of charge. dq i dt Voltage and Current (continued) The relationship between voltage and current in a circuit element defines that circuit element. Both voltage and current have associated polarities. These polarities determine the direction of power flow.

Ideal Basic Circuit Element Three attributes of an ideal circuit element: There are only two terminals Described mathematically in terms of current and/or voltage Cannot be subdivided into smaller components i + v - 1 2

Voltage Polarity Definitions + v - i 1 2 Positive v voltage drop from 1 to 2 or voltage rise from 2 to 1 Negative v voltage drop from 2 to 1 or voltage rise from 1 to 2 Current Polarity Definitions

+ v - i 1 2 Positive i Positive charge flowing from 1 to 2 Negative charge flowing from 2 to 1 Negative i Positive charge flowing from 2 to 1 negative charge flowing from 1 to 2 Passive Sign Convention +

v - i 1 2 Whenever the reference direction for the current in an element is in the direction of the reference voltage drop, use a positive sign in any expression that relates voltage to current. Otherwise, use a negative sign. Power and Energy dw dw dq p

vi dt dq dt Power associated with a circuit element is consumed by that circuit element when the value of power is positive. Conversely, power is generated, or produced by the element if the value consumed is negative. Expression of Power + v - i

i 1 2 + v - 1 2 p vi p vi i v +

i 1 2 p vi v + 1 2 p vi