What Are Resistors

What Are Resistors

The resistor is a passive electronic component that acts to reduce the flow of current and at the same acts to lower voltage levels within circuits. A passive component is a component that do not require power or source of energy in order to carry out its intended function or purpose. Other examples of passive components are capacitors and inductors.


Resistor is the most widely used electronic components in both electronic and electrical world. It can be found in almost  all electronic devices and electrical networks. The relationship between the voltage applied across a resistor and the current through it is given by  V  = IR. The resistance of a resistor is measured in ohms. The international symbol for resistor is a rectangular shape. In the USA, it’s a zigzag line.

Symbol for fixed resistor

International Resistor Symbol

Symbol for fixed resistor

American Resistor Symbol



Types Of Resistors

Resistors can be divided into 3 types which include:

I. Fixed resistor

II. Variable resistor

III. Resistor dependent on physical quantity

I. Fixed resistor is sub divided into 7 types, they are:

• Carbon composition

• Carbon film

• Metal film

• Metal oxide film

• Wirewound

• Foil

• SMD resistor

II. Variable is Sub divided into 3 types, they are:




III. Resistors dependent on physical quantity can be sub divided into 4 types, they are:

Photo resistor (LDR)

Thermistors (NTC and PTC)

Varistor (VDR)

Magneto resistor (MDR)

Resistor Applications

The applications and uses of resistors are very wide. The applications and uses of resistors depends on the type of resistor being use. The general applications and uses of resistors include:

• They are used in adjusting the volume level on a radio.

• They are used as fuse in some circuits.

• They are used as light sensors.

• They are used as temperature sensors in fire alarm

• They are used in timer and oscillator circuits

• They are used to control amount of voltage entering a part of a circuit.


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