Electronics 1

ELECTRONICSBy the end of the topic, the learner should be able to:

Define the term 'electronics'State its applications in the real

life situationMention the 3 electronic bandsDifferentiate, using energy

band theory, the following:(a) Insulators(b) Semiconductors(c) Conductors

©2013 David Owino 1

DEFINITION OF ELECTRONICS

Electronics is the branch of physics that deals with the emission and effects of electrons and the operation of electronic devices.

OR

Electronics refers to the science of electrons emissions and their behavior in semi-conductors.

OR

Electronics is the study of electronic circuits and their applications.


ELECTRONIC DEVICES

RadioTelephoneTelevisionCell phonesComputers and laptopsElectric kettleRefrigeratorSpeakers & microphonesSwitchesElectric iron

NB: The above devices use electrical components


ELECTRICAL COMPONENTS

DiodesTransistorsVacuum tubesTransformersResistorsCapacitorsIntegrated circuits (ICs)Inductors


COMPONENTS MOUNTED


CONT…


DIODE


CIRCUIT SYMBOL FOR A DIODE


TRANSISTORS


CIRCUIT SYMBOL FOR TRANSISTR


VACUUM TUBES

Amplifies electronic signals


TRANSFORMER


CIRCUIT SYMBOL


RESISTOR


CARBONRESISTORS

CIRCUIT SYMBOL FOR RESISTOR


CAPACITOR


CAPACITOR

©2013 David Owino 17POWERSTATION

CIRCUIT SYMBOL FOR CAPACITOR


INTEGRATED CIRCUIT


CIRCUIT SYMBOL FOR ICs


APPLICATIONS OF ELECTRONICS

Communication Medical services Domestic devices Entertainment


SUMMARY

The functioning of electric components is based on the behavior of semi-conductors

The components are mounted on circuit boards and are interconnected by a conductor

For safety reasons, electrical components are always insulated using an insulator

The electrical conductivity of insulators, conductors and semi-conductors is explained using energy band theory


ENERGY BAND THEORY

It postulates that when two or more atoms are brought closer to each other, the energy level split into smaller energy levels called bands

NB: The theory is better understood by studying the structure of an atom


ATOMIC STRUCTURE


M

L

K

EXPLANATIONElectrons spin around the

nucleus in the energy levels, marked K,L and M

The outermost energy level containing valence electrons splits more easily into many bands than the inner levels

The (1) splitting of energy levels into bands (2) inter band distance dictate the electrical, optical and magnetic properties of a given material


ELECTRONIC BANDS

1.Valence band (V.B): contains valence electrons

2.Conduction band (C.B): contains conduction electrons

3.Forbidden band: the gap between C.B and V.B

NB:Forbidden band distinguishes; insulators, conductors and semiconductors


INSULATORSMaterials which do not allow electric charges to pass through them

EXAMPLESPlasticsRubberDry wood


CONT…An insulator has a large energy

gap, Eg


C.B (empty)

Eg(Energy Gap)

V.B (completely filled)

EXPLANATIONA tightly bound electron in the

V.B requires large amount of energy to dislodge it from the parent atom and make it cross the forbidden energy gap to find a place in C.B

This amount of energy if supplied to an electron in crystal will break down the crystal

The absence of electrons in the C.B renders a material poor electrical conductor


Important pointsInsulators have infinitely high resistance (resistivity) to the flow of electric current

Increase in temperature or addition of impurities to insulators has no effect on their conductivity

Insulators are used as a cover material for conductors


CONDUCTORSMaterials which allow the passage of charges

EXAMPLESCopperSilverAluminumGraphiteNB: Conductors can either be good or poor


Good(e.g copper)has many free electrons

Poor(e.g. graphite)has less free electrons

CONT...V.B and C.B overlap


V.B (partly filled)

C.B (almost completely filled)

EXPLANATIONElectrons move freely from

partly filled V.B to C.BMany electrons in the C.B are

free for electric conductionThe flow of current in

conductors is by the movement of electrons

NB: a)A rise in temperature increases

the vibrations of the atoms which interferes with electron flow

b)There4, the resistance of conductors increases with temperature


SEMICONDUCTORS

Their electrical properties fall between those of conductors and insulators

EXAMPLESSiliconGermaniumNB: semiconductors form the basis of diodes, transistors and integrated circuits which have wide application


CONT…Has narrow forbidden band

compared to that of insulators


C.B (almost no electron)

Eg

V.B (almost completely filled)

EXPLANATION• An increase in temperature

increases the chance of an electron moving from V.B to C.B• When an electron in the V.B is

liberated to cross over to C.B a hole is created in the V.B

NB: a hole is regarded as +ve due to the absence of electron


ILLUSTRATION


Electron

Another electron within the V.B jumps into the hole, thereby creating another hole

The hole created subsequently filled by yet another electron and the process continues

Electron

HoleElectronHole

CONT…A hole is therefore seen to be

moving in the V.B, generating a hole/convectional current

The flow of electrons in the C.B constitutes electron current

The total current flow in semiconductors is due to flow of electrons and holes

NB: The electrical resistance of semi-conductors reduces with increase in temperature.


BYEMR. DAVID OWINO

END OF PRESENTATION

WELCOME TO

PART II


Education

Electronics 1