Basic Electrical Engineering

Lecture # 01

Course Instructor:Engr. Sana Ziafat

Grading Policy

Final Exam: 40% Mid term Exam 20% Assignments 5% Quizzes: 10% Labs25%

•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

• Electric CircuitsSchaum’s Outlinesby: 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 youCheck you weight Read your watchTake 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

From the previous slide, state the tool (s) you would use to measureA. temperature ____________________B. volume ____________________

____________________C. time ____________________D. weight ____________________

Solution

From the previous slide, state the tool (s) you would use to measureA. temperature thermometerB. volume measuring cup,

graduated cylinderC. time watchD. 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

Stating a Measurement

In every measurement there is a

Number

followed by a

Unit from measuring device

Learning Check

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 is1) 1.5 yards 2) 6 feet 3) 2 meters

B. The volume of saline in the IV bottle is1) 1 liters 2) 1 quart 3) 2 pints

C. The mass of a lemon is1) 12 ounces 2) 145 grams3) 0.6

pounds

Solution

A. John’s height is3) 2 meters

B. The volume of saline in the IV bottle is

1) 1 liter

C. The mass of a lemon is2) 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

In fo rm a tio n a t th e fo u n d a tio n o fm o d e rn s c ie n c e a n d te c h n o lo g yfro m th e P h y s ic s L a b o ra to ry o f N IS T

D e ta ile d c o n te n ts

V a lu e s o f th e c o n s ta n ts a n d re la te d in fo rm a tio nS e a rc h a b le b ib lio g ra p h y o n th e c o n s ta n ts

In -d e p th in fo rm a tio n o n th e S I, th e m o d e rnm e tric s y s te m

G u id e lin e s fo r th e e x p re s s io no f u n c e rta in ty in m e a s u re m e n t

A b o u t th is referen ce. F eed b ack.

P riv a c y S ta te m e n t / S e c u rity N o tic e - N IS T D is c la im e r

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