Basic Electrical Engineering Lecture # 01 Course Instructor: Engr. Sana Ziafat

Grading Policy Final Exam: 40% Mid term Exam 20% Assignments 5% Quizzes: 10% Labs 25%

Quizzes may be announced or unannounced. Exams are closed-book and extremely time limited. Exams consist of design questions, numerical, maybe true-false and short answer questions.

TEXT BOOKS Electric Circuits by J.W. Nilson & Susan A. Rediel Schaum’s Outlines by: M Nahvi

Objectives of the Course To impart the basic knowledge of electric circuits To know about various measuring instruments To introduce basic electrical concepts and laws

Agenda Basics of electric circuits Measuring system/SI Unit Ideal Basic circuit element Basic electric circuit quantities

Measurement You are making a measurement when you Check you weight Read your watch Take your temperature What kinds of measurements did you make today?

Standards of Measurement When we measure, we use a measuring tool to compare some dimension of an object to a standard.

Some Tools for Measurement

Learning Check A. temperature ____________________ From the previous slide, state the tool (s) you would use to measure A. temperature ____________________ B. volume ____________________ ____________________ C. time ____________________ D. weight ____________________

Solution From the previous slide, state the tool (s) you would use to measure A. temperature thermometer B. volume measuring cup, graduated cylinder C. time watch D. weight scale

International System Of Units Is a decimal system based on 10 Used in most of the world Used by scientists and hospitals Based on seven defined quantities Defined quantities are combined to form derived units.

Units in the Metric System length meter m volume liter L mass gram g temperature Kelvin K

In every measurement there is a Unit from measuring device Stating a Measurement In every measurement there is a Number followed by a Unit from measuring device

Learning Check A. The patient’s temperature is 102°F. What is the unit of measurement in each of the following examples? A. The patient’s temperature is 102°F. B. The sack holds 5 lbs of potatoes. C. It is 8 miles from your house to school. D. The bottle holds 2 L of orange soda.

Solution A. °F (degrees Fahrenheit) B. lbs (pounds) C. miles D. L (liters)

Learning Check Identify the measurement in SI units. A. John’s height is 1) 1.5 yards 2) 6 feet 3) 2 meters B. The volume of saline in the IV bottle is 1) 1 liters 2) 1 quart 3) 2 pints C. The mass of a lemon is 1) 12 ounces 2) 145 grams 3) 0.6 pounds

Solution A. John’s height is 3) 2 meters B. The volume of saline in the IV bottle is 1) 1 liter C. The mass of a lemon is 2) 145 grams

Derived Units Force equals mass time acceleration: newton is defined as unbalanced force that imparts an acceleration of 1 meter per second equal to a 1 kilogram mass. Work results when force works over a distance: Joule is equivalent to newton-meter Power is rate at which power is done: watt is joule per second

Electric Circuits Interconnection of electrical components Elementary quantities in the analysis of electric circuits are: 1. electric current 2. voltage

Electric charge and current Charge is bipolar, meaning electrical effects are described in terms of positive and negative charges. Time rate of change of charge is known as electric current: i(t) = dq(t)/dt where i and q are current and charge respectively. Basic unit of charge is ampere (columb per second) One ampere is equivalent to 1 columb charge moving across a fixed surface in 1 second.

Volatge If a unit positive charge is moved between two points then the energy required to move it is the difference in energy level between the two points and is defined as voltage. v= dw/dq, where as ‘w’ and ‘q’ are work and charge respectively Unit of voltage is volts, 1 volt= 1joule/coulomb= newton-meter/coulomb

Basic Circuit Element It has only two terminals It cant be further sub divided It is described mathematically in terms of current and voltage

Passive sign convention Whenever the direction for the current in an element is in the direction of the reference voltage drop across the element use a positive sign in any expression that relates the voltage to the current

Circuit Measurements Electric Current - Flow of electrons through a material Electrical Potential – Similar to potential energy (lifting something higher against the force of gravity gives it greater potential to do work, increasing its potential energy.) When given the opportunity, objects will move from higher potential energy to an area of lower potential energy Electrical potential is related to their electrical fields and not to height – as electrons build up on one side they “want” to flow to an area w/ less potential

Voltage Voltage – causes current to flow through an electrical circuit Volt – unit of measure to measure this potential A Voltage Source (battery or generator) is required to maintain the electrical potential in a circuit.

Electrical Current Water flowing thru a pipe depends on more than the angle of the pipe. It also depends on the length of the pipe, diameter of the pipe and if the pipe is clogged or open. Electrical Current is measured in Amperes Amount of Electrical Current ( amps) depends on more than just Voltage, it depends on the Resistance found in the circuit.

Energy and power Output of a system is often non electrical and is expressed in terms of energy or power. p=dw/dt Unit is watt and watt= joule/sec p=vi….. How?????????

Readings Chapter 1: 1.2, 1.4, 1.5, 1.6 (Electric Circuits) By James W. Nilson

Q & A