Resistance And Resistor (Part # Two: Let's start to buy our first component))

Before taking about ,what is resistors and how to you it and more .....

We need first to take in types of material

Types of material according to its electrical conductivity:

1. Conducting materials

in this type of material , the conductivity is high and have low resistivity such as metal as a general example.

2. Non-Conducting materials (Low Conductors and insulators)

in this type the opposite thing will be , it has law conductivity and low resistivity such as wood .

3. intermediate Conductive materials (Semi Conductors)

we won't to talk in it now

but , why does the conducting material has high conductivity , and low conducting material has low one ?

conductivity can be measured by free electrons in outer orbits in metal , the more the free electrons the more the current and low resistance (form ohm's law I=V/R) .

in high conducting materials , there are higher nombers of electrons than the lower one ( oh natural laws # 2) , this will cause higher resistance of low conducting material than high conducting materials .

From Now , we will divide our topic into two sections

1. Defining the " Resistor"

2. Some from Practical .

Section # 1 : Defining What is "Resistor"

after defining the "Resistance" , what do you think the resistor is ?

Resistor : is an electrical component that resist the current passing through it by producing voltage @ its terminals proportionally related with this current , so we can control current or voltage .

What is the Difference between "Resistance" and "Resistor" ?

resistance: the action of opposing the current (any conductor have a resistance)

resistor : an electrical component which has a certain resistance (we can say : this resistor has a resistance of ........ )

we can conclude this by , we put a a specific (constant) resistors as an electrical components to make some reistance in the circuit , in order to control current and voltage according to ohm's law .

For more understanding (English language lesson)

Resistance is a Noun that describes the naturals of the materials , but Resistors is an actor of an action (by by adding th "OR" prefix in the end of the verb "Resist" we will have "Resist-or" (Resist+or=Resist-or) for example "Visit-or .......etc.")

Note : When it comes actual circuit designing, dealing with components or physical board designing, these two words become interchangeable.

For example, if you say "a resistor of 22 ohms" or you say "a resistance of 22 ohms" both are acceptable.

Resistors electrical symbol:

Examples of Resistors :

Note : resistors also can be measured by the power that can dissipate from circuit in the shape of heat , and the power dissipated cab be calaculated from : P=I^2*R (See ohm's circle )

Resistor values - the resistor colour

code

1

Ω

is quite small so resistor values are often given in k

Ω

and M

Ω

(why..?).
1 k

Ω

= 1000

Ω

, 1 M

Ω

= 1000000

Ω

.

Resistor values are normally shown using coloured bands.
Each colour represents a number as shown in the table.

Most resistors have 4 bands:

• The first band gives the first digit.
• The second band gives the second digit.
• The third band indicates the number of zeros.
• The fourth band is used to shows the tolerance (precision) of the resistor, this may be ignored for almost all circuits but further details are given below.

This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.
So its value is 270000 Ω = 270 kΩ.
On circuit diagrams the

Ω is usually omitted and the value is written 270K.

Find out how to make your own Resistor Colour Code Calculator

Small value resistors (less than 10 ohm)

The standard colour code cannot show values of less than 10. To show these small values two special colours are used for the third band: gold which means × 0.1 and silver which means × 0.01. The first and second bands represent the digits as normal.

For example:
red, violet, gold bands represent 27 × 0.1 = 2.7Ω
green, blue, silver bands represent 56 × 0.01 = 0.56 Ω

Tolerance of resistors (fourth band of colour code)

The tolerance of a resistor is shown by the fourth band of the colour code. Tolerance is theprecision of the resistor and it is given as a percentage. For example a 390 resistor with a tolerance of ±10% will have a value within 10% of 390Ω, between 390 - 39 = 351Ω and 390 + 39 = 429Ω (39 is 10% of 390).

A special colour code is used for the fourth band tolerance:
silver ±10%, gold ±5%, red ±2%, brown ±1%.
If no fourth band is shown the tolerance is ±20%.

Tolerance may be ignored for almost all circuits because precise resistor values are rarely required.

For more understanding of Resistors color codes , see this video( pling # 3)

Now, you can go to buy some resistors from electronics shop , go now and buy nomber of resistors with various values .