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4.1


Thermionic





emission





is the process of



emission of electrons




from a heated metal’s



surface.






"To the electron -- may


it never be of any use


to anybody." -- JJ.

Thomson's






cathode simple





ray A beam of electrons tube of


moving at high speed




in a vacuum. cathode ray

















amazing Physics with Teacher Alina 2

The properties of cathode rays:













Negatively charged
Travel in straight lines and cast sharp shadows

particles (electron)
+ kinetic



energy
Travel at very

high speed

















cause fluorescence























Deflected by electric and





magnetic fields












amazing Physics with Teacher Alina 3

Factors that influence






the rate of thermionic





emission:







EFFECT ON THE RATE OF THERMIONIC

FACTOR

EMISSION




Temperature of the When the temperature of the cathode




cathode increases, the rate of thermionic emission




increases.




Surface area of the A larger surface area of the cathode increases




cathode the rate of thermionic emission.




Potential difference The rate of thermionic emission is unchanged,




between the anode when the potential difference increases, but




and cathode. the emitted electrons accelerate faster towards




the anode.









amazing Physics with Teacher Alina 4

STRUCTURE OF THE CATHODE RAY OSCILLOSCOPE











to avoid the air particles


or molecules collide with

emits the electron beam


electrons









to heat up


the



filament






heats up the cathode






Transmission of energy in cathode ray:





Electrical energy → Kinetic energy + light energy + heat energy






1

mv = eV v = velocity of electron
2

2 V = Potential difference between Anode and Cathode (EHT)


e = Charge on 1 electron = 1.6 x 10 C
-19
2 eV m = mass of 1 electron = 9 x 10 kg
-31
v =




amazing Physics with Teacher Alina m 5

The properties of electron streams in a



Maltese cross cathode ray tube GO


















6 V heater is





switch



on a shadow


of cross is



seen
























The shadow is formed by the light rays from the heated filament










CONCLUSION: light rays travel in a straight line









amazing Physics with Teacher Alina 6

The properties of electron streams in a



Maltese cross cathode ray tube GO



























a green



shadow



of cross is





3 kV EHT seen





switch on








The shadow is formed by the cathode rays




Electrical energy → Kinetic energy + light energy + heat energy








CONCLUSION: cathode rays cause fluorescence









amazing Physics with Teacher Alina 7

The properties of electron streams in a



Maltese cross cathode ray tube GO





using





Fleming’



s left




hand



rule










North pole (bar a green

magnet) is



brought close to shadow



the cathode rays distorted

(move downwards)













CONCLUSION: cathode rays can be deflected by





magnetic field








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Deflectiontube GO



























The cathode



ray deflected




upwards































CONCLUSION: cathode rays Negatively charged





cathode rays can be deflected by electric field










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Uses of GO




Cathode ray oscilloscope










Vertical scale = Y-gain control



The uses of






cathode-ray






Period = time for 1 oscilloscope



complete oscillation




Frequency, are:




1 1.To measure a D.C

f=


T or A.C voltage




2.To measure a




short time intervals




3.To display the



Horizontal scale = Time base waveform







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Display wave
Cathode ray oscilloscope forms and




measuring voltage


from a DC source


using a
electronic
CRO







































































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Display wave
Cathode ray oscilloscope forms and




measuring voltage



Type of power Time-base switched Time-base switched from a DC source



supply connected electronic using a


to Y-input of CRO off on CRO












No


input
















DC


power supply














AC


power supply









amazing Physics with Teacher Alina 12

example What is the value of the dc voltage if the Y-gain




control is 1 V/div ?




Measuring Potential Difference using the CRO











Time-base switched off
4



3


2


1 1 V /div













dc voltage = 4 div x ! "



#$%



= 4 V



























amazing Physics with Teacher Alina 13

example What is the value of the dc voltage if the Y-gain




control is 1 V/div ?




Measuring Potential Difference using the CRO











Time-base switched on
4



3


2


1 1 V /div













dc voltage = 4 div x ! "



#$%



= 4 V



























amazing Physics with Teacher Alina 14

example Calculate the peak voltage and




peak to peak voltage.



Y-gain = 3 V/div
Measuring Potential Difference using the CRO

















peak voltage







= 4 div x ! " 1 V



#$% p



= 12 V V pp






















peak to peak voltage







= 8 div x ! " = 24 V


#$%





amazing Physics with Teacher Alina 15

example Y-input of an CRO setting at




20 V/div and 5 ms/div





Solve problems based on the CRO display









peak voltage





V p 1 5 ms / div = 4 div x !" # = 80


$%&





peak to peak voltage

V pp = 8 div x !" # = 160






$%&















Period (T) Frequency






,
= 8 div x ' () = = , = 25
$%& - .." 0 ," !"


= 40 = 4.0 10 *+ s







amazing Physics with Teacher Alina 16

example The length between the two crests is 3 cm.



(Given 1 division = 1cm)




time-base is set to 5 ms/div
Solve problems based on the CRO display







Period (T)







= 3 div x ' ()

$%&

= 15 = 0.015 s

1





Frequency





,
= = , = 66.67


- ".,'









When the frequency of the Frequency double (2 times)



wave is double, what is the ∴ Period decrease (2 times)



!
length between the two Length = = 1.5 cm



crests? "






amazing Physics with Teacher Alina 17

4.2

material that has electrical



semiconductor conductivity that is between that





of a conductor and an insulator




characteristic Example of


semiconductor

has good electrical
as insulator at s are:


conductivity at a) Silicon



b) Germanium


c) Boron



d) Tellurium


e) Selenium


































Comparison between energy gap in insulator, semiconductor and conductor







amazing Physics with Teacher Alina 18

free electrons carry negative charge

a process of adding holes carry positive charge



a small amount of




impurities

to a semiconductor






doping

3P BAGI










5N APA 3 à trivalent






P à p-type


Doping material à B = Boron


5 à pentavalent A = Aluminium



N à n-type G = Gallium

Doping material à A = Antimony I = Indium


P = Phosphorus Role of doping material à atom receiver


A = Arsenic Majority charge carrier à holes



Role of doping material à atom donor Minority charge carrier


Majority charge carrier à free electrons



à free electrons


Minority charge carrier à holes



amazing Physics with Teacher Alina 19

n-type p-type










Combination of p-type semiconductor with n-type




semiconductor with produce a semiconductor Diode











Anode (+) cathode (-)






















amazing Physics with Teacher Alina 20

Semiconductor

diode is to allow


current to flow


through it in one


direction

only


HOW?
































Depletion layer






neutral region which has no charge



carriers and poor


conductor of electricity




The wider the depletion layer,




no current flow









amazing Physics with Teacher Alina 21

Forward current flow






one
bias direction
























n-type semiconductor is connected to





negative dry cell






Depletion layer is narrow


(resistance diode decrease)








Current flow






Bulb light up










amazing Physics with Teacher Alina 22

Reverse



Current only flow



in one bias




direction





















n-type semiconductor is connected to





positive dry cell






Depletion layer is wide


(resistance diode increase)








No Current flow






Bulb not light up







amazing Physics with Teacher Alina 23

Rectification is a process to convert an alternating Half wave



current into a direct current by using a diode rectification










B C







A













E





D










current will only flow in the first half-cycle when the diode in




forward bias (A à B à C à D à E)







The current is blocked in the second half-cycle when the diode is in




reverse bias (E à D à C à B à A)









amazing Physics with Teacher Alina 24

Rectification is a process to convert an alternating FULL



current into a direct current by using a diode Half wave

rectification



























































In the first half, the In the second half, the




current flows from current flows from




P → B → D → Q Q → C → A → P









amazing Physics with Teacher Alina 25

When the current pass through the resistor and
The uses of capacitor, the capacitor is charged and
capacitor



stores energy.






When there is no current pass through the




resistor and capacitor, the capacitor



discharge




The energy from it is used to produce voltage across the



resistor.






As a result it produces a smooth dc output












































amazing Physics with Teacher Alina 26

To amplify the current



transistor or act as a switch







4.3




































































npn transistor pnp transistor






amazing Physics with Teacher Alina 27

Transistor as a current amplifier















Current
Small I à bigger I C Amplification:

B


when I = 0, I C = 0 #$

B
= &



I ≠ I c #$ '

B






I C > I B



To limit




I E > I C > I B the I B









I E = I C + I B
























amazing Physics with Teacher Alina 28

Transistor as a potential divider


















V 1




V











V 2



















%
%
)
V = % & % ) V V = % & % ) V
(
2
1
(
(








V + V = V


1
2






amazing Physics with Teacher Alina 29

The uses of transistor LIGHT


CONTROLLED





SWITCH
















































































amazing Physics with Teacher Alina 30

The uses of transistor LIGHT


CONTROLLED





SWITCH
















































































amazing Physics with Teacher Alina 31

HEAT CONTROLLED SWITCH


















1 4 I flow

C
Temperature ↑







Resistance of 5








is




↑
activated
2







R↑ V ↑ 6


B


∴ I flow

B
3 Transistor is




on is on















amazing Physics with Teacher Alina 32

SOUND AMPLIFIER















Sound waves with higher


5 amplitude is produced
























2 Capacitor




allows the varying I flow



current flow it C



4

I changed

B



3






1 converts





audio (sound) signal à electrical





amazing Physics with Teacher Alina 33

has one or more input signals but only

4.4 Logic one output signal




Gate










1.Logic gates as switching


circuits in electronic




systems



2.Input and output signal of he



logic gates can be either





high (logic 1) or







low (logic 0).

































amazing Physics with Teacher Alina 34

AND SYMBOL:






Gate






X=A•B


BOOLEAN EXPRESSION:













TRUTH TABLE: CIRCUIT:

















































amazing Physics with Teacher Alina 35

OR SYMBOL:






Gate






X=A+B


BOOLEAN EXPRESSION:













TRUTH TABLE: CIRCUIT:

















































amazing Physics with Teacher Alina 36

To inverse the



input signal




NOT SYMBOL:






Gate





X=A



BOOLEAN EXPRESSION:













TRUTH TABLE: CIRCUIT:

















































amazing Physics with Teacher Alina 37

NAND Gate NOR Gate











SYMBOL:















BOOLEAN




EXPRESSION: X=A • B X=A + B














TRUTH TABLE:



































amazing Physics with Teacher Alina 38

COMBINATIONS OF LOGIC GATES



example



1








































TRUTH TABLE: INPUT OUTPUT



A B P Q Y





0 0 1 1 1




0 1 1 0 0





1 0 0 1 0





1 1 0 0 0









amazing Physics with Teacher Alina 39

COMBINATIONS OF LOGIC GATES



example



2








































TRUTH TABLE: INPUT OUTPUT



A B R S Y





0 0 1 0 0




0 1 1 1 1





1 0 1 1 1





1 1 0 1 0









amazing Physics with Teacher Alina 40

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amazing Physics with Teacher Alina 41