مراجعة الفيزياء 3 ثانوى تجريبى ولغات

1. AHMED HEKAL
CHAPTER (8)
MODERN ELECTRONICS

2. Mr. Ahmed Hekal
1
Chapter 8
A. Definitions
1- Semi-Conductors:
- Materials that fall between conductors and insulators ,their conductivity increase by raising their
temperature
2- Crystal :
- regular arrangement of atoms in solid state
3- Hole:
- Free space left by electron in a broken bonds in the semi-conductor crystal
4- Dynamic (Thermal) Equilibrium
- It’s the state in which number of broken bonds in 1 sec equal number of mended bonds in the semi-
conductor crystal and this always make number of free electrons equal number of holes for each specific
temperature
5- Pure Semi-conductor:
- Semi-conductor in which concentration of n (free electrons) = concentration of P (holes) at any temperature
6- Impurity Atom:
- Atom of a trivalent element or pentavalent element added to a pure semi-conductor crystal to increase its
conductivity
7- Doping: (Adding impurities)
- Adding a trivalent element or pentavalent element to a pure semi-conductor crystal of tetravalent element
to increase concentration of free electrons or holes in it
8- P-type Semi-conductor
- Semi-conductor doped with a trivalent element to make the concentration of holes (p) greater than
concentration of free electrons (n)
9- N-type Semi-conductor
- Semi-conductor doped with a pentavalent element to make the concentration of free electrons (n) greater
than concentration of holes (p)
10- Law of Mass Action:
- The product of concentration of free electrons (n) and holes (p) = Constant , this constant doesn’t depend on
impurity type and it equals the square of concentration of free electrons Or concentration of holes in the
pure semi-conductor crystal at constant temperature
11- Diode:
- Two adjacent crystals one of them is n-type and the other is p-type
12- Diffusion Current:
- Current results in diffusion of free electrons from region n to region p and diffusion of holes from region p to
region n
13- Transition (depletion) Region:
- It’s the region that are free of charges carriers and it exists in the contact area between the two crystals in
diode
14- Drift Current:
- Current results in the internal electric field between positive ions towards (n) region and negative ions
towards (p) region in the contact area between the two crystals and it opposes the diffusion current

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15- Potential Barrier:
- The lowest potential in the contact area between the two crystals that prevent more diffusion of electrons
and holes to the lower concentration region of them
16- Distribution Factor (ratio) coefficient αe
- Ratio between the collector current to Emitter current when potential difference between base and
collector is constant
17- Amplification Factor βe
- Ratio between the collector current to base current when potential difference between emitter and
collector is constant
18- Analog Electronics
- Electronics that deal with natural quantities as they are, and convert them to electrical signals of continuous
decimal numbers (1, 2, 3…)
19- Digital Electronics
- Electronics that deal with natural quantities but convert them to non-continuous codes of zeros and ones
where zero represents low logic and one represents high logic
20- Logic Gates
- Parts of electronic circuits of modern devices that perform the logic operations on the digital signals (like
NOT, AND, OR )
B. What’s meant by?
1- The Potential Barrier of diode = 0.3 V
- It means that the lowest potential in the contact area between the two crystals that prevent more diffusion
of electrons and holes to the lower concentration region of them = 0.3 V
2- Distribution coefficient αe = 0.98
- Ratio between the collector current to Emitter current when potential difference between base and
collector is constant = 98 : 100
3- Amplification Factor βe = 46
- Ratio between the collector current to base current when potential difference between emitter and
collector is constant equals = 46 :1
C. Diagrams
Relation between Diagram Law and slope
A. Current Intensity and Potential
difference at forward and backward
bias-connection in diodes
Diode allows current when
forward connection and prevents
current when backward connected
B. Vout and Vin when using Transistor as a
key
When Vin is high Vout is low and
vice versa

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C. IC and IE when V between Base and
collector is constant
Slope = αe = Ic/IE Ic = αe IE
D. IC and IB when V between Emitter and
collector is constant
Slope = Ic/IB
D. Deductions
1- Ratio of Amplification in Transistor
- αe = Ic/IE Ic = αe IE
- IB= IE - Ic
- Ic/IB = αe IE / (IE - αe IE )
- αe/(1- αe)
E. Usages:
1- Specialized electronics devices Used as sensors for the for environmental factors as heat, light,
pressure and pollution
2- Diode 1- Open key if it’s backward connected and closed key if it’s
forward connected
2- Rectifying AC to DC to charge cars batteries and mobiles
chargers
3- Transistor 1- As Amplifier
2- As a Switch
4- Analog to Digital Converter - Converts continuous electrical signals to digital non-
continuous signals in the receiving device
5- Digital to Analog Converter - Converts digital non-continuous to continuous electrical
signals in the receiving device
6- Analog Devices - Electronics that deal with natural quantities as they are,
and convert them to electrical signals of continuous
decimal numbers (1, 2, 3…)
1- Microphone
2- Legacy Video Camera
3- Legacy T.V.s
7- Digital Devices 1- Cell Phones (mobiles)
2- CDs
3- Computers
4- Digital channels
8- Logic Gates Used in PC circuits
F. Comparisons

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1- N-Type and P-Type Crystals
N-Type P-Type
Concentration of
charges carriers
Free electrons greater than holes Holes greater than Free electrons
Type of impurity
atom
Donor atom and it’s atom of pentavalent
element as Antimony or Phosphorus shares
with 4 bonds and lose one electron and
became positive + ion
Acceptor atom and it’s atom of trivalent element
as Boron or Aluminum shares only in 3 bonds
and gains one electron and became negative -
ion
Charges carriers Electrons Holes
Donors Impurities Acceptors Impurities
Shape of crystal after Doping
Impurity Valence Pentavalent atoms like
Phosphorus(P) and Antimony (SB)
Trivalent atom as boron (B) and
Aluminum (AL)
Impurity work action Shares with 4 electrons in forming
bonds and one extra electron is left
Shares only with 3 electrons in bonds
and there is one hole left needs an
electron
Charges carrier type Free electrons Holes
Impurity atom after doping Became positive ions Became negative ions
Crystal Type after doping n-type p-type
Relation bet. n,p N > P P > N
At dynamic equilibrium N = p + ND
+
P = n + NA
-
Diode Ohmic Resistance
Structure 2 adjacent n , p crystals Coil of wire of a specific resistivity
Charges Carriers Free electrons and holes Free electrons
Current Intensity Current flows in one direction and
vanished ‫يتالشى‬ in opposite direction
Current can flow in the two directions

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Heat Effect Resistance decreases and
conductivity increases
Resistance increases and conductivity
decreases
Forward bias connection Backward bias connection
Work Action
Crystal p is connected to positive
pole of battery and crystal n is
connected to negative pole of the
battery
Crystal n is connected to positive pole
of battery and crystal p is connected to
negative pole of the battery
Effect of external voltage on diode Direction of external voltage of
battery opposites direction of
internal field in the depletion region
so it weakens it
Direction of external voltage of battery
same as direction of internal field in the
depletion region so it weakens it
Voltage of Diode Less than potential barrier More than potential barrier
Thickness of depletion (transition)
region
Decreases in cause of repulsion
between similar poles
Increases in cause of attraction
between different poles
Diode resistance Very small Very high
Current Intensity High (current passes) Low (current stops)

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PNP Transistor NPN Transistors
structure Base is negative -
Collector and emitter are positive +
Base is positive +
Collector and emitter are negative -
Symbol in electrical circuit
Similar properties NPN as an amplifier (common base) NPN as an amplifier (common emitter)
Connection method 1- Emitter E is connected with Base B forward connection
2- Collector C is connected with Base B Backward connection
Electrons Movement
direction
1- Electrons are released from emitter of type (N) to Base of type (P) and spread
for an interval of time until it’s picked up by Collector of type (N)
2- Collector N picks up electrons as it’s connected to positive pole of battery
Different properties NPN as an amplifier (common base) NPN as an amplifier (common emitter)
Circle Diagram
Operation Part of electrons are consumed in
occupying the holes of Base, so collector
current is less than emitter current (IC= αe
IE) and αe is always less than 1 so in this
case transistor is not used in amplifying
current but used in amplifying the
electrical power
Electrons of collector are repulsed with
negative pole of batteries so the two
currents of electrons are met at the
emitter and moves towards the collector
so if a small electrical signal is placed in
base current so its effect appears larger in
collector current by ratio of e where
e= IC/IB so transistors are used here in
amplifying current and voltage and
electrical power

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NOT Gate AND Gate OR Gate
Equivalent circuit
A key connected in
parallel
When it’s opened, lamp
is on and when it’s
closed lamp is off
Two keys connected in
series
Lamp is not on except
the two keys are closed
Two keys connected in
parallel to each other
Lamp is on if one of them is
closed
Number of I/Ps and O/Ps One I/P
One O/P
Two or more I/Ps
One O/P
Two or more I/Ps
One O/P
Truth Table
Input Output
0 1
1 0
Input Output
A B
0 0 0
0 1 0
1 0 0
1 1 1
Input Output
A B
0 0 0
0 1 1
1 0 1
1 1 1
Logic Operation Reverse Multiply (output is 1
when and only when the
2 inputs are 1)
Add (output is 1 if any one
of the inputs was 1)
Symbol

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Transistor as a key in case of ON Transistor as a key in case of OFF
1- It’s connected in electrical circuit where emitter is common
2- VCC = VCE + ICRC
Where VCC is Battery voltage and VCE is potential difference between collector and emitter and IC is the collector
current and RC is circuit resistance
When connecting Base B to a positive or high voltage,
a large current IC is passing in collector circuit so value
of ICRC is large and VCE is small (output is small value)
It means that transistor passes current of base
because (Vin > Vout)
When connecting Base B to a negative or low voltage, IC will
decrease in collector circuit and ICRC is small so VCE increases
(output is large value)
It means that transistor doesn’t pass current of base because
(Vout> Vin)
G. Briefly Notices
1. Conductivity for Semiconductors
- Semi-conductors are not a good conductors in low temperatures so it’s conductivity can be improved by
1- Raising temperature of semi-conductor
2- Doping (adding impurities of trivalent as Boron or pentavalent elements as Antimony
2. Properties of pure crystal (Pure Silicon)
1- The highest (last) level of each atom is complete by electrons at 0 kelvin
2- Electrons of internal levels are strongly coherent with nucleus but the outer electrons have higher
degree of freedom to move through the interatomic spaces inside the crystal
3- At low temperatures (specially at 0 kelvin), Bonds are intact ‫سليمة‬ so there are no free electrons inside
the crystal and no conductivity
4- By raising temperature some bonds are broken and some electrons are freed and when an electron
leaves its position it leaves a hole and this is not considered an ionization because atom will picks up
another electron rapidly and returns to neutral state
5- By continue raising temperature, number of free electrons and holes increases so conductivity increases
6- Electrons moves randomly inside the crystal to occupy holes that arises ‫عن‬ ‫تنشأ‬ breaking bonds
7- Energy needed to break a bond = energy resulting in building the bond whether this energy is thermal or
optical (light)
3. Types of Electronics components:
1- Simple components: as Resistance R , Induction Coil L , capacitor C
2- More complex components: Diodes, Transistors
3- Special components: photo-electric devices and control devices

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4. Diode:
1- In a crystal of type P , the concentration of holes p is larger than concentration of electrons n and in a
crystal of type n, the concentration of electrons n is larger than concentration of holes p
2- when the two crystals are contacted, holes p and electrons n are spreading from higher concentration
region to lower concentration so holes transfer from crystal p to crystal n and electrons transfer
from crystal n to crystal p and current passes called Diffusion Current
3- Holes of region p cannot cover all electrons in region n , and electrons of region n cannot cover all
holes of region p
4- Two regions empty of electrons and holes are generated around the contact area, these regions have
positive ions towards crystal n and negative ions towards crystal p these empty regions called
Transition or (depletion) Region
5- When crystal of type n lose some electrons it gains positive potential and crystal of type p gains a
negative potential because it receives electrons, so an electrical field generated and its direction from
crystal n (positive potential) to crystal p (negative potential) causing a current called Drift Current
6- By continue transferring electrons and holes from higher concentration region to lower concentration
region the potential difference between the two crystals increases until it reaches a value which
prevents this transfer of electrons from n to p and the Diffusion Current = Drift Current and
in this case the potential difference is called Potential Barrier
H. What’s happened in these cases?
1- Increasing number of broken bonds using heat , for the semi-conductor crystal
- Number of free electrons and number of holes increase so conductivity increases
2- Doping a pure Silicon crystal with atoms of Boron
- Boron atom gain an electron and became negative ion so concentration of holes increase inside crystal and
became crystal of type p and its conductivity increases
3- Doping a pure Silicon crystal with a pentavalent element atoms
- The pentavalent atom loses an electron and became a positive ion so the concentration of free electrons
increases and it the silicon became a crystal of type n and it conductivity increases
4- Contacting crystal of type p with a crystal of type n to form a diode
- Holes spread from p to n and free electrons spread from n to p , so positive ions increase towards n crystal
and negative ions increase towards p crystal this happens on the two sides of contact so a potential barrier
is generated and prevents transfer of electrons and holes
5- Connecting diode as forward-bias connection in the electrical circuit
- The external electrical field weakens the internal field and decreases the thickness of depletion region and
potential of diode decreases under the potential barrier and the resistance if diode decreases so a current
will pass
6- Connecting diode as backward-bias connection in the electrical circuit
- Increase internal electrical field and decrease thickness of depletion region, increase the potential barrier,
increase resistance of diode so no current will pass
7- Connecting diode to AC current
- Diode will rectify the direction of AC current, it will pass in one direction only and not pass in the other
direction

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I. Give reason
1- When raising temperature of semi-conductor its conductivity will increase
- Because raising temperature leads to increase the broken bonds and release more free electrons which
increases the electrical conductivity
2- The semi-conductor atom which has a broken bond isn’t considered an ion
- As soon as the bond is broken, the hole will picks up another electron from another bond or from a other
free electrons to be stable
3- The pure silicon crystal is completely insulating at 0 Kelvin
- Because at low temperatures all bonds are intact so there is no free electrons
4- At thermal equilibrium there is no increase in free electrons or holes
- Because number of broken bonds in 1 second equals number of mended bonds so number of free electrons
and number of holes is constant at a specific temperature
5- When adding atoms of Antimony to a crystal of silicon, its conductivity increases
- Because Antimony is pentavalent element and Silicon is tetravalent so antimony share silicon with 4
electrons in its outer shell and 1 electrons remain free which increases conductivity
6- Semiconductor crystal of type n or p is neutral
- Because in type p: sum of positive charges (p) = sum of negative charges for electron (n) + sum of negative
charges for Acceptor ions NA
-
, And
- in type n: sum of negative charges (n) = sum of positive charges for electron (p) + sum of positive charges for
Donor ions ND
+
7- Semiconductors are used as sensors for environmental factors around them
- Because semiconductors are very sensitive for the surrounding factors (light, pressure, temperature,
radiation pollution )
8- In case of forward-bias connection the diode allows current flow
- Because the external electric field of the battery is in opposite direction of internal electric field of the diode
(at the contact region) so it weakens this field and the thickness of the depletion region decreases which
leads to decrease the potential barrier so electrical current will pass
9- In case of backward-bias connection the diode prevents the current flow
- Because the external electric field if the battery is in the same direction of internal electric field of the diode
(at the contact region) so it strengthens this field and the thickness of the depletion region will increase
which increases the potential barrier so electric current will not pass
10- Diode can be considered a circuit switch “key”
- Because in case of forward–bias connection current will flow “closed switch” and in backward-bias
connection current cannot flow “open switch”
11- Diode and electrical resistance are different
- If we used Ohmmeter in measuring electrical resistance ,reading doesn’t change if the current is reversed,
but in diode the current flows in one direction so reading of Ohmmeter is high in a specific direction of
current and it changes to zero if the current flows in the opposite direction
12- The effect of high temperature is different for diode and ohmic resistance
- By raising temperature more covalent bonds are broken which leads to increase number of free electrons
which increase the conductivity “free electrons” and decrease resistance, but in ohmic resistance by
increasing temperature its resistivity increase and conductivity decrease
13- Ohmmeter is used to check the diode operability
- Diode operation is perfect if it allows current in a specific direction (forward-bias) and if it prevents current
in the opposite direction (backward-bias)

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14- Diode is used in rectifying the direction of AC current
- Because diode allows current flow in one direction which is considered the first half of AC current cycle in
case of forward bias connection but it prevents the current in the other direction which is considered the
second half of AC cycle so the resultant voltage is uni-directional
15- The thickness of base should be very small in transistors
- To decrease the consumption of electrons that populates holes existing in base, this will allow the majority
of electrons to reach collector and the value emitter current to be near the value of collector current
16- Transistor is used as a switch “key”
- When connecting transistor “npn” in the common emitter circuit, so if the base voltage is positive or high
,current will flow in collector and transistor is considered a closed key “ON”, and if the base voltage is
negative or low the collector current is cut off so transistor is considered an open key “OFF”
21- Distribution constant “factor” αe is approximately 1 and the amplification constant “factor” βe is very high
- Because base is very thin and has a little impurities so it consumes a very small part of emitter current so
emitter current is approximately equal collector current and αe = IC/IE is approximately 1 , and base current is
very small βe= Ic/IB so βe is very high
22- Digital electronics is preferred more than analog electronics
- In digital electronics we can get rid of random currents and noise which resulting in random motion of
electrons of different voltage values(1,2,3,4,5,6,…) and digital electronics only deals with two values 0,1
So digital electronics produce a pure and regular signals

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Laws
Transistor
As a key
VCC= VCE + ICRC
As an amplifier:
Amplification Factor
βe = IC/IB = αe / (1 - αe)
Distribution Factor
αe = IC/IE = βe/ (1 + βe)
Emitter Current
IE = IC + IB
(AND) means: multiply (2 or more I/Ps and 1
O/P)
(OR) means: add (2 or more I/Ps and 1 O/P)
(NOT) means: reverse value (1 I/P and 1 O/P)
Laws
N-Type Crystal
Electrons concentration
n = ND
+
Holes concentration
p = ni
2
/ND
+
Crystal returns to stable state when
NA
-
= ND
+
P-Type Crystal
Holes concentration
p = NA
-
Electrons concentration
n = ni
2
/NA
-
Crystal returns to stable state when
NA
-
= ND
+
Mass Action Law
np = ni
2
Where ni
2
is the concentration of
electrons or holes in the pure silicon
crystal