What is Electric Resistance

A circuit is a closed path where electrons move to generate current. To answer the question, what is electric resistance of an object, is to know the measure of its opposition to the flow of current. Its reciprocal is conductance, measuring the ease with which current passes.









Current is the path used to transmit current. The circuit includes a device that provides energy to the charged particles that make up the current, such as a battery or generator. Circuit is an important concept with practical application in our daily lives. This is a very simple concept that contains three different components—a closed loop of electrical energy, equipment, and conductive materials.


The resistance of an object depends to a large extent on the material it uses. Objects made of electrical insulators such as rubber tend to have very high resistance and low conductivity, while objects made of electrical conductors such as metal tend to have very low resistance and high conductivity. This relationship is quantified by resistivity or conductivity. However, the nature of the material is not the only factor in resistance and conductance; it also depends on the size and shape of the object, because these properties are extensive rather than dense. For example, if the wire is long and thin, the resistance is higher, and if the wire is short and thick, the resistance is lower. All objects resist current, except for superconductors, which have zero resistance. The resistance R of an object is defined as the ratio of the voltage V across it to the current I through it, and the conductance G is the reciprocal.


A substance that can flow electricity is called a conductor. The conductive material of a particular resistor used in the circuit is called a resistor. Conductors are made of highly conductive materials, such as metals, especially copper and aluminum. On the other hand, resistors are made of various materials, depending on factors such as the required resistance, the energy required to dissipate, accuracy and cost. The resistance of a given object depends mainly on two factors: what material it is made of, and its shape. For a given material, finding out what electric resistance is will determine how the resistance is inversely proportional to the cross-sectional area; for example, the resistance of a thick copper wire is lower than that of other identical thin copper wires. In addition, for a given material, the resistance is proportional to the length; for example, a long copper wire has a higher resistance than other identical short copper wires. The resistance R and conductance G of a conductor with a uniform cross-section.


There are two basic types of resistors.

  1. Linear Resistors

These resistance values vary with the applied voltage and temperature, called linear resistance. In other words, a resistor whose current value is proportional to the applied voltage is called a linear resistor. Generally, there are two types of resistors with linear characteristics.


  • Fixed Resistors
  • Variable Resistors
Fixed Resistors

Fixed resistor is a resistor which has a specific value and we can’t change the value of fixed resistors.

Types of Fixed resistors


  • Carbon Composition Resistors
  • Wire Wound Resistors
  • Thin Film Resistors
  • Thick Film Resistors



Variable Resistors


As the name indicates, those resistors which values can be changed through a dial, knob, and screw or manually by a proper method. In these types of resistors, there is a sliding arm, which is connected to the shaft and the value of resistance can be changed by rotating the arm. They are used in the radio receiver for volume control and tone control resistance.


Types of Variable resistors


  • Potentiometers
  • Rheostats
  • Trimmers



  1. Non Linear Resistors

Nonlinear resistors are those resistors, where the current flowing through it does not change according to Ohm’s Law but, changes with change in temperature or applied voltage.

In addition, if the flowing current through a resistor changes with change in body temperature, then these kinds of resistors are called Thermistors. If the flowing current through a resistor change with the applied voltages, then it is called a Varistors or VDR (Voltage Dependent Resistors).

Following are the additional types of Non Linear Resistors.


  • Thermistors
  • Varisters (VDR)
  • Photo Resistor or Photo Conductive Cell or LDR



  1. Resistors in series: – when they are so connect) there equivalent resistance of combination is given by R = R1 + R2 + R

Resistors in Series


2. Resistors in Parallel: They are arranged side by side such that their corresponding ends join together at two       common junction e.g.

Resistors in Parallel

Note: To differentiate parallel from series, when all the right sides are connected to each other and all the left sides to each other, if is termed as parallel, while for series the left side is always connected to the right of the next resistor.

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