R = (PL)/A
Where, R = Resistance (W)
L = Length of the conductor (m)
A = Area of cross-section of conductor (m^2)
P = Specific resistance or resistivity of the material.
This resistance value of a resistor depends upon physical dimensions of the resistor and resistivity of the conducting material used.
Resistors are used in electronic circuits to:
- Limit the flow of current
- Provide load
- Produce a desired voltage drop.
- To control gain
- Fix time constants etc.,
Types of resistors
Resistors are broadly classified into two types on the basis of the nature of value of resistance.
- Fixed resistor
- Variable resistor.
The below image is a chart on the types of resistors, click on it to enlarge.
Fixed resistor
The fixed resistors are further classified into two types. They are
- High stability type
- General Purpose type
High stability type
High stability types are further classified into four types
- Cracked carbon resistors
- Metal film resistors
- Metal oxide resistors
- Wire wound resistors
General Purpose type
Carbon composition resistors are called general fixed resistors. They are two types.
- Solid cylindrical types
- Film types
Solid cylindrical type is divided into two types
- Un- Insulated molded type
- Insulated molded type
General purpose variable resistors
This is divided into three types
- Carbon composition variable resistors
- Wire Wound Variable resistors
- Precision type variable resistors
Precision type variable resistors
This is subdivided into
- Precision variable potentiometers
- Trimming potentiometers
Precision variable potentiometers
It is divided into two types:
- Film types
- Wire wound type
Trimming potentiometers
- Rectilinear
- Rotary
Use the above image to have a clear cut idea on classification of resistors