Electronics 1
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Transcript of 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
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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.
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ELECTRONIC DEVICES
RadioTelephoneTelevisionCell phonesComputers and laptopsElectric kettleRefrigeratorSpeakers & microphonesSwitchesElectric iron
NB: The above devices use electrical components
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ELECTRICAL COMPONENTS
DiodesTransistorsVacuum tubesTransformersResistorsCapacitorsIntegrated circuits (ICs)Inductors
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APPLICATIONS OF ELECTRONICS
Communication Medical services Domestic devices Entertainment
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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
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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
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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
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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
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INSULATORSMaterials which do not allow electric charges to pass through them
EXAMPLESPlasticsRubberDry wood
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CONT…An insulator has a large energy
gap, Eg
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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
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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
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CONDUCTORSMaterials which allow the passage of charges
EXAMPLESCopperSilverAluminumGraphiteNB: Conductors can either be good or poor
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Good(e.g copper)has many free electrons
Poor(e.g. graphite)has less free electrons
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
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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
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CONT…Has narrow forbidden band
compared to that of insulators
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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
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ILLUSTRATION
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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.
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