beng1113 principle of electrical and electronics chapter 1 (week 1) faculty of electronic and...

BENG1113PRINCIPLE OF ELECTRICAL AND ELECTRONICS

Chapter 1 (week 1)

FACULTY OF ELECTRONIC AND COMPUTER ENGINEERING

Chapter 1: Introduction to Electricity2

Learning Outcome

• Upon completion of this chapter, student should be able to:– Describe the basic structure of atoms– Define nucleus, proton, neutron and electron– Describe ionization and free electron– Define conductor, semiconductor and insulator– Convert decimal no to standard or engineering

notation


Chapter 1

• Subtopics:1. Atomic structure

2. SI units, Scientific and Engineering notation

3. Electrical charges

4. Electrical quantities - voltage, current and resistance

5. Active and passive components

6. Basic electrical instruments

7. Basic circuit measurement

8. Electrical safety.

Atomic Structure

• ATOM : The smallest particle of an element that possesses the unique characteristics of that element.

• PROTON : The basic particle of positive charge.

• ELECTRON : The basic particle of negative charge.

• NEUTRON : An uncharged particle found in the nucleus of an atom.

• NUCLEUS : The central part of an atom containing protons and neutrons.

4

Balanced Atom

• an equal number of electrons and protons.

• no electrical charge.


Valance Electrons

• VALANCE SHELL : The outermost shell of an atom.

• VALANCE ELECTRONS : Electrons in the valance shell.

• The valance electrons contribute to chemical reactions and bonding within the structure of a material and determine its electrical properties.

Ionization

• Since electrons are lighter than protons and are outside the nucleus, they can be easily moved from atom to atom to form electrons

• When an atom absorbs energy, the valance electrons possess more energy and they can actually escape from the outer shell and becoming free electrons.

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The periodic table

Exercises

1. How many electrons contains in the valence shell for the elements below.

a) Sodium

b) Chlorine

2. Draw the atomic structure of the copper atom (no.of electrons = 29).


CONDUCTORS

• A material that easily conduct electrical current.

• A CONDUCTOR has 1 to 3 valence electrons in the outermost shell. Therefore its electrons tend to move to other atom.

• Most metals are good conductors and the best conductors are single-element materials such as copper, silver, gold and aluminium.

INSULATORS

• A material that does not conduct electrical current under normal conditions.

• Most good insulators are compounds rather than single-element material such as rubber, plastics, glass, mica, and quartz.

• An insulator is any material with 5 to 8 valence electrons in the outer ring.

SEMICONDUCTORS

• A material that is between conductors and insulators in its ability to conduct electrical current. It has exactly 4 valence electrons.

• A semiconductor in its pure (intrinsic) state is neither a good nor a good insulator.

• The most common single-element semiconductors are silicon, germanium, and carbon.

• The most common compound semiconductor is gallium arsenide.

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SI units [1]

length mass

time

electric current

temperature

luminous intensity

amount of substance

meter

kilogram

second

ampere

Kelvin

candela

mole

m

kg

s

A

K

cd

mol

Quantity Unit Symbol

Table 1-1


• This is the units that are derived from the fundamental units except for current since it is a fundamental unit

current

charge

voltage

resistance

power

ampere

coulomb

volt

ohm

watt

A

C

V

W


Table 1-2


• All magnetic units are derived from the fundamental units [1].

flux densitymagnetic flux

magnetizing force

magnetomotive force

permeability

tesla

weber

ampere-turns/meter

ampere-turn

webers/ampere-turns-meter

ampere-turns/weber

T

Wb

At/m

At

Wb/Atm

At/Wbreluctance


Table 1-3


Scientific notation

• Provides a convenient method for expressing large and small numbers1=100 1/10 =0.1 =10-1

10 =101 1/100 =0.01 =10-2

100 =102 1/1000 = 0.001 =10-3

1000 =103 1/10,000 =0.0001 =10-4

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Mathematical Operation

• To perform addition or subtraction using powers of ten, the power of ten must be the same for each term:

• Multiplication

• Division

• Power

nnn BABA 10)(1010

( 10 )( 10 ) ( )( ) 10n m n mA B A B

1010

10

nn m

m

A A

B B

( 10 ) 10n m m nmA A

Exercises

1. Express each number in scientific notation

a) 200

b) 5000

c) 85000

d) 3,000,000

e) 4750



2. Express each of the following numbers in scientific notation:

a) 0.2

b) 0.005

c) 0.00063

d) 0.000015

3. Express each number as a regular decimal number:

a) 1 x 105

b) 2 x 103

c) 3.2 x 10-2

d) 2.5 x 10-6

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Engineering notation

• Similar to scientific notation• A number can have from one to three digits to

the left of the decimal point and the power-of-ten exponent must be a multiple of three [1]

• For example;33000 = 3.3 x 104 = 33 x 103

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• Matrix prefix– Specific powers of ten in engineering notation

have been assigned prefixes and symbols [2]

10-3

10-6

10-9

10-12

10-15

milli

micro

nano

pico

femto

m

n

p

f

peta

tera

giga

mega

kilo

1015

1012

109

106

103

P

T

G

M

k


• Metric unit conversions– Larger unit: move the decimal point to the

right– Smaller unit: move the decimal point to the

left– e.g.

0.15mA = 150µA

Exercises

1. Perform the mathematical operation;a) 6300 + 75000

b) 0.0096 – 0.000086

c) (0.0002)(0.000007)

d) (340,000)(0.00061)

e) 0.00047/0.002

f) 690000/0.0000013

g) (0.00003)3

h) (90800000)2


2. Example 1-8 [1]: express the following numbers in engineering notation

a) 82,000

b) 243,000

c) 1,956,000

d) 0.0022

e) 0.000000047

f) 0.00033

3. Example 1-10 [2]: Convert the following• 20 kHz to megahertz• 0.01ms to microseconds• 0.002km to millimeters


Electrical Charges

• Charges of opposite signs (one negative and one positive) attract one another.

• Charges of the same sign (both positive and both negative) repulse one another.


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Electrical Charges

• The unit of charge [1]:– The unit of charge is denoted by Coulomb– One coulomb is the total charge possessed

by: 6.25 x 1018 electrons or protons– A single electron has a charge of 1.6 x 10-19

C and a single proton has a charge of +1.6 × 10-19 C.

– Total charge;

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number of electrons

6.25 10 electrons/CQ


Exercises

1. How many Coulombs of charge do 93.8 x 1016 electron represent?

2. How many electrons does it take to have 3C of charge?

Electrical Force

• Electrical forces act between charges

• Q1 and Q2 = charge on the objects (in C)• D = distance between objects (in meters)• k = a constant = 8.99 x 109 N m2/coul2

• The strength of the electrical force decreases as the distance between the charged objects increases

D

QkQFelectrical

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Basic Electrical Components and Instuments

• Resistors• Resistors resist, or limits, electrical current in a circuit.

• Capacitors• Capasitors store electrical charge; they are used to

block direct current (dc) and pass alternating current (ac).

• Inductors• Inductors, also known as coils, are used to store

energy in an electromagnetic field; they serve many useful functions in an electrical circuit

• Transformers• Transformers are used to magnetically couple ac voltages from one

point in a circuit to another, or to increase or decrease the ac voltage. Companies such as TNB use huge transformers to change voltages for high-voltage transmission lines.

• Electronic Instruments• There are four basic electronic instruments normally found in

laboratory and will be use throughout the lab session for this course. These instruments include:

• • DC power supply - provide current and voltage to power electronic

circuits.• Function generator – provide electronic signals.• Multimeter – with its voltmeter, ammeter and ohmmeter functions for

measuring voltage, current and resistance, respectively• Oscilloscope – observe and measure ac voltages.

Voltage

• Voltage is the electrical force that moves electrons through a conductor. The pressure also known as EMF (Electro Motive Force) that pushes electrons.

• Voltage is expressed as;

• V = voltage in volts (V)

• W = energy in joules (J)

• Q = charge in coulombs (C)

• One volt is the potential difference (voltage) between two points when one joule of energy is used to move one coulomb of charge from one point to the other.

Q

WV

Exercises

• Determine the voltage• 10J / 1C• 5J / 2C• 100J / 25C

• If 50J of energy are available for every 10C of charge, what is the voltage?

• 500J of energy are used to move 100C of charge through a resistor. What is the voltage across the resistor?

Voltage Source

• Battery: A battery is a type of voltage source that convert chemical energy into electrical energy. A battery consists of one or more electrochemical cells that are electrically connected.

• four basic components: a positive electrode, a negative electrode, electrolyte and a porous separator.

Electrolyte

Porous separator

Negative electrode Positive electrode

- +

• Solar cells: The operation of solar cells is based on the photovoltaic effect (light energy is converted directly into electrical energy). It has 2 layers of different types of semiconductive materials joined together to form a junction. When one layer is exposed to light, many electrons acquire enough energy to break away from their parent atoms and cross the junction, and thus a voltage is developed.

• Generator: Electrical generators convert mechanical energy into electrical energy using a principle called electromagnetic induction. A conductor rotated through a magnetic field, and a voltage is produced across the conductor.

• Electronic power supply: Electronic power supply does not produce electrical energy from some other from energy. They simply convert the ac voltage from wall outlet to a constant (dc) voltage.

• Measuring instrument: A VOLTMETER

Current

• Current is the movement or flow of charge (electrons) from the negative end of the conductor to the positive end

• Current in a conductor material is measured by the number of electrons (amount of charge) that flow past a point in a unit of time

t

QI

I = current in Ampere (A)Q = charge of the electrons in coulombs (C)t = time in seconds (s)

• One ampere (1A) is the amount of current that exists when a number of electrons having a total charge (1C) move through a given cross-sectional area in one second.

• Electricity with electrons flowing in only one direction is called Direct Current (DC). It flows in one direction, positive to negative, steadily. A graph of a DC voltage or current would look like a flat horizontal line.

• Electricity with electrons flowing back and forth, negative - positive- negative, is called Alternating Current, or AC. It literally changes direction at a certain rate, called its frequency, measured in Hertz.

• Ordinary household electricity in Malaysia is 240 VAC, 50 Hz. A graph of 240 VAC is a sine wave. AC can be used at it is in light bulbs and motors, but for electronic devices, it must be stepped down to a lower voltage and then converted to DC. For example, the CPU in many computers typically takes 3.6 volts DC.

• Measuring instrument: Ammeter

Exercises

• 10C of charge flow past a given point in a wire in 2s. What is the current in amperes?

• If there are 8A of direct current through the filament of a light bulb, how many coulombs have moved through the fillament in 1.5s?

Resistance

• Resistance, R, is the force that reduces or stops the flow of electrons.

• Opposite to current and measured in Ohms ()• The schematic symbol is shown below

• Conductance, G, is the reciprocal of resistance.• The unit is in Siemens (S)

• Measuring instrument: Ohmmeter

1G

R

http://en.wikipedia.org/wiki/Image:Resistor_symbol_America.svg

Resistor Colour Codes

Resistance value, first three bands:

First band 1st digitSecond band 2nd digit*Third band multiplier (number of zeros following the 2nd digit)

Color

Black

Brown

Red

Orange

Yellow

Green

Blue

Violet

Gray

White

Gold

SilverFourth band tolerance

* For resistance values less than 10 , the third band is either gold or silver. Gold is for a multiplier of 0.1 and silver is for

a multiplier of 0.01.

No band

0

1

2

3

4

5

6

7

8

9

5%

10%

Digit

20%

100

101

102

103

104

105

106

107

108

109

10 -1

10 -2

Multiplier

1% (five band)

5% (four band)

Tolerance

2% (five band)

10% (four band)

• What is the resistance and the tolerance?

Alphanumeric Labeling

• Two or three digits, and one of the letters R, K, or M are used to identify a resistance value.

• The letter is used to indicate the multiplier, and its position is used to indicate decimal point position.

Power

• When current is forced through a resistance, work is said have been done. Power is the rate of working, represented by "P". Energy is the capacity to do work.

• Power is energy per time or the rate of working, represented by "P". The standard unit used in electricity is the Watt (W) = 1 Joule / second.

• The amount of power consumed by an electrical device is the rate at which it dissipates energy.

R

VRIIVP

22

Basic Circuit Measurement

• Multimeter

Digital Multimeters (DMM) Analog Multimeter

• Meter symbols

Measuring Current

• Most analog ammeters have a number of possible settings for the maximum possible current that can be measured; for example: 2 A, 200 mA, 20 mA, 2 mA. You should always start by turning the setting to the highest possible rating (for example, 2 A). If the ammeter reading is too small from the selected scale, then you can reduce the scale to get the reading. It is important not to overshoot the maximum value that can be read.

• For example, if the current is about 75 mA, then the ammeter would be set to the 200 mA scale for the most accurate reading. Setting to the 20 mA scale would overload the ammeter and most likely open its internal fuse.

Measuring Voltage

Measuring Resistance

Measured Numbers

• Error : The difference between the true value and the measured value

• Accuracy : The degree to which a measured value represents the true or accepted value of a quantity. A measurement is said to be accurate if the error is small.

• Precision : The repeatability or consistency of a measurement

Chapter 1: Introduction to Electricity

53

• Resolution– The smallest increment of quantity that the

meter can measure. The smaller the increment, the better the resolution.

0.001V0.01V

54

Passive Components

• Passive components: Components that do not supply voltage or current – Examples

• Resistors • Capacitors • Inductor• Transformer

Color bands

Resistance material(carbon composition)

Insulation coating

Leads

MicaFoil

FoilMica

Foil

FoilMica

Foil

Tantalum electrolytic capacitor (polarized)

Mica capacitor_

Active Components

• The components that have their own power source.

• Passive components are used in conjunction with active components to form an electronic system– Voltage and current sources

• Battery, Generator, Fuel cell

• Transistor• Integrated Circuit (IC)

Electrical Safety

• Electrical shock :when voltage is applied across two points on human body , it caused current to flow through the body

• The severity of the resulting electrical shock depends on the amount of voltage and the path that the current takes through the body

• Effects of current on the human body:– Depends on voltage and body resistance.

• Body resistance:– Typically between 10kΩ and 50kΩ– The moisture of the skin and body mass also affects the

resistance between two points

57

Chapter 1: Electrical Safety

• Some of safety precautions :– Avoid contact with any voltage source. Turn off power

before you work on circuits when touching circuit parts is required.

– Do not work alone. A telephone should be available for emergencies.

– Remove rings, watches, and other metallic jewelry when you work on circuits.

– Always wear shoes and keep them dry

– Do not stand on metal or wet floor

beng1113 principle of electrical and electronics chapter 1 (week 1) faculty of electronic and...

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valence electrons

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atomic structure atom

copper atom

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