Basic Electronic


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Basic Electronic

First chapter includes:

Static electricity and its history
Coulomb's law
Categorizing objects
Current electricity
Electric current intensity
The concept of electrical resistance
The concept of voltage
Ohm law
The concept of electric power
Things related to power
Resistor and its types
Detecting resistance amount from color bands
Reading resistance from numeric codes and Latin letters
The concept of tolerance (error percentage) of resistors
Resistors’ standard amounts
The final problems of the chapter

Electricity and electronic principle
Static electricity and its history

The origin of human knowledge of electricity can be estimated to be from 600 BC, when Greek philosopher Thales discovered that, amber can attract light objects by rubbing. And the name electricity comes from “electron”, the Greek word for amber.
Attracting light objects with amber

Creating static electricity in objects by rubbing was experienced until the end of 18 century by many scientists including “Otto von Guericke”. In those experiments, they realized that: some of the objects have the Property of attracting or repelling other objects by rubbing. In other words, they can apply force to each other. Existence of the force is because of the existence of «Electrical load» in objects. That’s why it’s called «Electric force».

Coulomb's law:
The reason of force existence between 2 loaded objects can be justified like this: there is an »Electric field« around each loaded object and even though it can’t be seen by the eyes, it’s real. For the first time a French physicist, “Coulomb” could experimentally measure the force between loaded objects in 1785. He also got a relation for the force amount which is:

Force between 2 loaded particles depends on load amount of each one, distance between 2 loads and also environment material that the 2 loaded particle are in.
Electrical load unit is called Coulomb and it is equivalent to electrical load of 6.24 * 1018 electron.
Coulomb. -1.6*10-19 An electron is approximately equals to
The negative sign next to the number (-1.6) doesn't have any effect on its amount and it’s only to show the negative load of electron.

Categorizing objects:
:Objects in nature are electrically divided into three categories

A: Insulator or non-conductor: The objects in which there are no free electrons. Glass, Mica, Rubber and Wood are among them. Electricity in those objects are static and they stay (static) at one point



B: Conductor: The objects that have a large number of free electrons, such as copper, silver and aluminum. The generated electricity is uniformly distributed over the metal surface due to the ability of the electrical load to move in the metal.
Aluminum bars

Copper cables

C: Semiconductor: The objects that are electrically between conductors and insulators. In other words, they are the elements that have 4 electrons in their outer shell of atom. Like silicon and germanium:
Molecular structure of silicon

Germanium Transistor

Current electricity: In 1799, Italian physicist Alessandro Volta was able to generate electricity by his own voltaic pile and send a continuous current in the wires. He called this electricity "current electricity".

:Electric current intensity
:The amount of electrical load changes in time unit is called electric current. Which is calculated with the formula bellow

If the movement of electrons is uniformly in a steady direction in the wire, the current is called D.C and its amount is calculated with the formula below.

t: Time in terms of second
Amount of electrical load in terms of Coulomb q:
I: Electric current in terms of Ampere

The number of electrons that pass from a point of circuit determines the amount of current flow from the circuit. The higher the number of the electrons, the more the “current flow”.

Amperage definition: An ampere is electric current of wire and one Coulomb electrical load (6.24*1018 electron) flows from its specific section surface in one second.
Electric current is represented by the Latin letter I (the first letter of Intensity) and its unit is indicated by A ampere. The smaller amperage units are: One thousandth of ampere=1mA and One millionth of amp=1μA.

m= milli

The concept of Electrical resistance
The electrical resistance
is a factor that prevents the flow of electric current. The resistor is represented by the Latin letter R (the first letter of Resistance) and its unit is in terms of ohm with the Latin letter Ω
Larger ohm units

One thousand ohm= one Kilo Ohm= 1KΩ
One million ohm= one Mega Ohm= 1MΩ

The concept of voltage

The potential difference between two points of circuit is the amount of energy that electrical load consumes to move from one point to another.

v: Voltage in terms of volt
w: Energy in terms of Joule
q: Electrical load in terms of Coulomb

Definition of Volt: one volt is the potential difference of two points of circuit. When one Coulomb electrical load (6.24*1018 electron)consumes one joule energy while moving from those two points, it would be one volt. Voltage is represented by Latin letter V (first letter of voltage) and its unit is indicated in terms of V volt.

Ohm’s Law
when current intensity I flows from resistor R, the potential difference V will be created in both sides of the resistor, and the amount is obtained :by the following formula

This law is named after its discoverer Georg Ohm.

Ohm triangle:

The resulting relationships of Ohm's law:

Concept of electric power
The work which is done in a time unit is called electric power which is obtained from the following relation:

P: Electric power in terms of watt
w: Energy in terms of Joule
t: Time in terms of second

.Electric power is represented by Latin letter P (first letter of Power) and its unit is indicated in terms of W watt

Allowed power, is the maximum power that a device can tolerate. The resulting relationships of power formula:

:As a result, the final formula of power is as follows

?Problem 1: What is resistance of a 100 watt light bulb

?Problem 2: What happens if we connect a 100 watt with 110 volt light bulb to a 220 volt power


:First solution: First, we calculate the resistance of the light bulb

The bulb burns due to quadrupled (4 times of) power

:Second solution: We calculate the allowed current of the bulb

.Bulb burns because current is doubled
Result: resistors burn, in case power and current intensity raise from the allowed limit

.Problem 3: Calculate the resistance of a 1000 watt electric heater compared to a 200 watt bulb


.Bulb resistance is 5 times of heater resistance
.Result: The higher the power of the consumer devices, the lower their resistance

?Problem 4: how much ampere does a 3300 watt air conditioner use


Air conditioner uses 15 ampere (the current)

🅰 types of resistors in terms of placement on PCB circuits

(Surface Mount Device (SMD
Surface Mount Technology (SMT)

They are placed on the surface.

Plated Through Hole (PTH)

Placing pin through a hole.

B: types of resistors in terms of usage on circuits
Fixed resistors 2. Adjustable Resistors 3. Variable Resistors 4. Array Resistors 5. Printed Carbon Resistors .1

Fixed Resistors
Fixed Resistors:

These resistors are divided into 2 types in terms of production (1- Wire wound 2- Composition)

A) Wire Wound Resistor
Types of wire wound resistors divide into Cement-Clay-Chinese resistors depending on their insulation. There is coil inside them. Wires are usually made of alloys (nickel-copper) / (nickel-chromium) / (nickel-chromium-aluminum)
.Wire wound resistors have lower ohm and higher power compared to composition ones and their size (Wire wound resistors) is also bigger

B) Composition
Composition Resistors include 1- Carbon composition Resistors 2- Carbon film Resistor 3- Metal film Resistor 4- Metal oxide film Resistor

Carbon composition Resistors: carbonic compositions (mixture of carbon powder) is formed (formwork) as dough with resin andresistant materials, and cooked in a furnace and covered with insulator. These resistors are small in size with high resistance but low tolerance, from one
fourth watts to two watts

Carbon film Resistor: This type of resistor is made of sedimentation of a thin layer of carbon on a ceramic bar, and groves will be created on the resistor for increasing its amount, then the set is covered with insulator

Metal film Resistor: This type of resistor is made on glass material bar and a thin layer of gold, platinum and silver (metals) is covered on it and then grooves will be created on the layer. The disadvantages of these resistors are expensiveness and power limitation (1 watt)
Metal oxide film resistor: This type of resistor is somehow like the metal film resistor, with a difference that, tin and antimony metal oxides are used instead of metal cover

Adjustable resistors: (knobs)
These resistors are used in radio, Television and audio devices as adjustable resistors (manually) in order to turn up and down volume or adjust brightness which are usually carbonic and wire types are used in high power
:Types of these resistors are
Potentiometer: A potentiometer is used to change the voltage

Rheostat: it is used to change the resistance

Trimmer: Instead of a moving handle, it has a groove which should be adjusted with a screwdriver

The way these resistors work is that they have two fixed and one variable pins. The resistance amount between the two fixed pins (2 side pins), which in fact determines the potentiometer’s amount, is a fixed amount. While the resistance between the pin in the middle and either of the side pins can be changed by a revolving axis (knob handle)

Variable Resistors (Varistor)
These types of resistors change without mechanical actions and they change under factors such as voltage, heat, light and magnetism, and are divided on the same basis
Symbolic circuit of Varistor

A) Voltage Dependent Resistor (VDR)
This type of resistor’s resistance changes depending on the amount of applied voltage and it is used to keep the voltage fixed in a point of circuit and its resistance decreases when voltage increases

B) Thermal Resistor (Thermistor)
:It is divided into two categories

Positive Temperature Coefficient (PTC)-
.A thermistor with positive thermal coefficient’s resistance amount increases when heat increases

.The impedance written on these resistors is measured at 25 degrees Celsius

Negative Temperature Coefficient (NTC)-
A thermistor with negative thermal coefficient’s resistance amount decreases when heat increases and is made of various oxides Fe2O3, MnO2, NiO. To neutralize undesirable changes of the currents and voltages of the elements by heat, it is used as thermostat to prevent the temperature from rising and to prevent the very high instantaneous current intensity and..

C: Light Dependent Resistor (LDR)
.Resistance amount decreases due to the intensity of light. And its main material is cadmium sulfide

:D: Magnetic Dependent Resistor (MDR)
The resistance amount of these resistors changes by applying the magnetic field, in a way that, by increasing the field, their ohm amount decreases

..E: There are other variable resistors which their resistance amount changes by humidity, gas

Array or Network resistors
The array resistor actually contains a set of several resistors inside a package, which are available both in SMD and PTH, and the internal resistance amounts are all equal. In logic circuits, they are being used to pull up and pull down the inputs and outputs, they are also used in LED circuits.
In SMD type, pins across from each other make separated resistors and they don’t have common pin
In the PTH type, a pin (which is marked) is the common pin, and each of the other pins make a resistor with the common pin.

Printed carbon resistors

These resistors are carbon mix type and are printed directly on fiber layers of PCB circuit. This type of resistor’s tolerance (error percentage) is high (even up to 30%) and it can’t be replaced

Detecting resistance amount from color bands

1- Four colors:

First and second bands = Numbers
Third band = coefficient or number of zeros
Fourth band = Tolerance or error percentage
The order of reading resistance amount

2- Five colors:

First, second and third bands= Numbers
Fourth band = coefficient or number of zeros
Fifth band = Tolerance (Error Percentage)
:The order of reading resistance amount

3- Body, end and point color: This type is the British standard (B.S) which was used in older devices
Body and end colors= numbers
Dot color= coefficient or number of zeros
Initial (beginning) color= Tolerance
The order of reading colors
Body- End- Dot
↑ ↑ ↑
Numbers Coefficient

:The order of reading resistance amount

Number colorCoefficient colortolerance color 4 colors
1= Brown1= black2%= Red
2= Red10= brown5%= Golden
3= Orange100= red10%= silver
4= Yellow1000= orange
5= Green10000= yellowtolerance color 5 color
6= Blue100000= Green0.1%= Purple
7= Purple1000000= Blue0.25%= Blue
8= Gray0.1= Golden0.5%= Green
9= white0.01= Silver1%= Brown
0= black2%= Red

4- Six colors: it's like 5 colors and the sixth color is the characteristic of the thermal coefficient which its number is expressed in terms of PPM or centigrade degree.

The order of reading resistance amount

5PPM= Purple
10PPM= Blue
15PPM= Orange
25PPM= Yellow
50PPM= Red

:How to read resistance amount from the numeric and letter codes
1- clear mode which means no code and password

:Ohm and tolerance and even the allowed power (maximum power) of resistors are written on them. Such as
15Ω 10% 2W
15ohm 2 watts resistor with 10% tolerance
330 ohm 10 wat resistor with 5% tolerance

2- 3 digit mode

4700Ω= 4.7 KΩ

3- 4 digit mode


4- A Latin letter and several digit mode




R= Ω= Ohm
K=KΩ= Kilo Ohm
M= MΩ= Mega Ohm

.Note: The Latin letter will be considered as decimal if it is placed between the digits or on the left side of the digits

5- 2 Latin letters and several digit mode

10KΩ with 5% tolerance (error percent)

0.27Ω with 1% tolerance

3.3MΩ with 10% tolerance

.Note: The first Latin letter will be considered as decimal if it is placed between the digits or on the left side of the digits

. second letter: tolerance. first letter: resistance Range
0.1% =BR= Ω Ohm
0.25% =CK= KΩ Kilo Ohm
0.5% =DM= MΩ Mega Ohm
F= 1٪
G= 2٪
H= 3٪
J= 5٪
K= 10٪
M= 20٪

Concept of the tolerance (error percentage) of resistor:
In the factory production line, making each resistor is associated with error. The accurate the resistor, the less its error percentage (tolerance). When resistor tolerance is said to be 5%, its amount will be calculated as follows

Error percentage+-resistance amount in terms of ohm
For example, a 10KΩ resistor with 10% error is calculated like this
10%of 10000 is 1000, so the resistor can vary from 9000Ω to 11000Ω

Standard amounts of resistors
Several base numbers have been selected as standard from one tens of resistance (eg, 0 to 10 ohm) for example, in standard E6, six base numbers (1- 1.5- 2.2- 3.3-4.7-6.8) are the existing resistances of the standard. Letter E is taken from beginning of the word European. You can see the full chart of standards below


:The final problems of the chapter
-if 100 mA current flows through a 2.2 Kilo ohm resistor, what would the voltage at both sides be?

R= 2.2 KΩ=2200Ω
I=100mA= 0.1A
V=R.I= 2200*0.1=220
voltage of both sides of the resistor V=220V

If voltage of both sides of a 1 Kilo ohm resistor is 12 volt, calculate its current-

?Voltage of both sides of a resistor is 3.3 volt and its current is 30 mA. What is the amount of resistance-

?A 100 ohm resistor that can tolerate current of 0.3 amps is required in an electric circuit. The following resistors are available for choosing-
?100Ω-10w) and (100Ω-7.5w) and (100Ω-5w) which one should be chosen)

(100Ω-10w) resistor is better, because allowed wattage limit needs to be more than power 9. Two other resistors will burn on the circuit.

?Calculate the allowed voltage of a 100 ohm resistor, if its allowed power is 2 watts-

?A flashlight LED with 300 MW power requires 50 mA to be able to turn ON. what is the LED's volt amount-

Evaluate your knowledge by answering the questions bellow:
What do you think is the difference between a 100 ohm ¼ watt resistor and a 100 ohm ½ watt resistor? Is it possible to place ¼ watt resistor in a circuit in which a ½ watt resistor is required? What about in reverse?

-Calculate the amounts of E12 series resistors from 1 ohm to 100 ohm?

-Calculate the amounts of resistors that are specified with following colors?

Fourth colorThird colorSecond colorFirst color

Fifth colorFourth colorThird colorSecond colorFirst color

-According to the tolerance of each resistor of previous problem, specify the maximum and minimum ranges of each one?

-Calculate amounts of the following resistance which are specified with the letter codes?