Basics of Resistor:


Resistors are basic two-terminal passive electronic components which implements a particular level of electrical resistance. The electrical resistance limits the flow electrons through an electric circuit. They act like passive components which means that they only consume power and can’t generate it. In different electronic circuits resistors are used for the adjustment of the signal levels, to reduce the flow of current, termination of transmission lines, division of voltages etc. Resistor with high power can dissipate many watts of electrical power. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity.

Note: Resistance of a resistor depends on their length (l), resistivity (ρ) and its cross sectional area (a) which is also known as laws of resistance … R = ρ (l/a) .

Resistor Units:

Ohm is used to measure electric resistance of a resistor. Ohm is represented by a greek symbol capital-omega: Ω. 1Ω is defined by the resistance between two points in a circuit where 1 volt(V) of potential energy will produce 1 ampere (1A) of current.

For larger and smaller values we will use S.I units Ω with prefix like giga, mega etc., to reading easier. It is common to see resistors in megaohm (MΩ) and kilohm (kΩ) and range and less range milliohm(mΩ). For example, a 5,000Ω resistor is equivalent to a 5kΩ resistor, and a 6,600,000Ω resistor can be written as 6,600kΩ or 5.6MΩ.

Notations and Symbol Used:

Resistor and Different Symbols of Resistors

Each resistor has one connection and two terminals. We will look at the three types of symbols that are used to represent the resistor.


The terminals of the resistor are each of the lines extending from the squiggle (or rectangle). Those are what connect to the rest of the circuit.

The resistor circuit symbols are usually enhanced with both a resistance value and a name. The value, displayed in ohms, is obviously critical for both evaluating and actually constructing the circuit.

Types of Resistors:

Resistors are available in different shapes and sizes. Common types that are available are through-hole and surface mount. A resistor might be static, standard resistor, special, or a pack of variable resistor.

Type of Resistors

Termination and Mounting:

Commonly there are two termination types available in resistors: surface mount or through-hole. These types of resistors are usually abbreviated as either PTH (plated-through-hole) or SMD/SMT (surface-mount-technology or device).

Through-hole come along with long and pliable leads which can be soldered on a prototyping board or PCB(Printed Circuit Board). Through-holes are more often used in prototyping, bread boarding or places where you would not solder tiny 0.6 mm long surface mounted resistors. Through-hole resistors usually take up much more space than their SMD counterparts because the long leads usually require trimming.

These resistor come in axial package. The power rating of resistor is related to the size of axial resistor. A common half watt resistor measures around 9.2 mm across, while smaller ¼  Watt resistor is about 6.3 mm long.

Surface-mount(SMD) resistors are small black rectangles, their one side is terminated with silver, shiny and smaller conductive edges. SMD are made so that they can sit over the printed circuit boards, where they are soldered on the landing pads. As the size of these resistors is small they are set on breadboards by the robots, and sent into ovens where the solder melts and fix them in proper place.

Resistor Composition:

Resistors can be constructed out of a variety of materials. Most common, modern resistors are made out of either a carbon, metal, or metal-oxide film. In these resistors, a thin film of conductive (though still resistive) material is wrapped in a helix around and covered by an insulating material. Most of the standard, no-frills, through-hole resistors will come in a carbon-film or metal-film composition.

Different types of materials can be used for the construction of resistors. These include metal, carbon or a metal-oxide film. In these resistors a thin film of conductive material is enveloped in a helix and is covered by insulating material.

Other through-hole resistors might be wirewound or made of super-thin metallic foil. These resistors are usually more expensive, higher-end components specifically chosen for their unique characteristics like a higher power-rating, or maximum temperature range.

Surface-mount resistors are usually either thick or thin-film variety. Thick-film is usually cheaper but less precise than thin. In both resistor types, a small film of resistive metal alloy is sandwiched between a ceramic base and glass/epoxy coating, and then connected to the terminating conductive edges.

Resistor Markings:

Resistors may not display the value outside but resistor color pattern through their resistance can be calculated. PTH resistors use a color-coding system (which really adds some flair to circuits), and SMD resistors have their own value-marking system.

Stay tuned with BYJU’S to learn more about resistors, electric circuit and much more.

Practise This Question

You are given 48 cells each of emf 2 V and internal resistance 1 ohm. How will you connect them so that the current through an external resistance of 3 ohm is the maximum?