Electricity and Resistance

Electricity plays a significant role in modern civilizations. Most of the things around us, our computers, lights, soldering irons, cell phones, air conditioners, fans, etc, directly or indirectly depends on electricity.  There are three important terms, which we should be aware of when we talk about electricity i.e. resistance, current, and voltage.

Electric current may be defined as the rate of flow of charge. This flow of charge occurs due to the difference in potential between two points in any material. Let us see what do we mean by resistance? Resistance can be defined as the opposition exerted by a substance to the flow of electric current. It is represented by the symbol ‘R’ and its S.I.unit is Ω (ohm).

Let us zoom into the wire and see what is exactly happening inside the wire? The atoms are arranged uniformly inside a wire forming a lattice structure called the metallic lattice.  These atoms of the metal wire have loosely bonded electrons. In an insulator or a bad conductor, the electrons of the atoms are held tightly.

In a case of potential difference in the wire, the electrons from the atoms jump out and leave positively charged atoms behind. There are two kinds of charges: positive charge and negative charge. As soon as a potential difference is created, electrons get aligned to each other and they move in one single direction as per the applied potential difference, but there are some positively charged atoms, which block the flow of electrons and try to attract the electrons towards themselves. Due to this, the flow of electric current gets reduced. This opposition to the flow of electrons by positively charged atoms is known as resistance. The resistance of a wire depends on many factors. Some of the factors are given below:

Factors affecting resistance:

  1. Area of cross section: If the area of cross section of a wire is small then the number of electrons passing through a particular point at a particular time interval will be less. If the area of cross section of a wire is increased then there will be a number of electrons passing through, in the same interval of time. Hence, there will be an increase in the current flow. Thus, the resistance of a wire is inversely proportional to the area of cross section of the wire.

 Area of cross section

  1. A length of wire: If the length of a wire is increased, then the number of positively charged atoms that attract the electrons also increases. This results in a decrease of current flow. Hence, the resistance is directly proportional to the wire length.

A length of wire

With respect to the above specifications, we can conclude that a short fat wire will be a good conductor of electricity.

To visualize the concepts of resistance and various factors affecting it with the help of an example, watch the video.


Practise This Question

The height of a mercury barometer is 75 cm at sea level and 50 cm at the top of a hill. Ratio of density of mercury to that of air is 104. The height of the hill is