Published by: BhumiRaj Timalsina

Published Date: 25 Jan 2022

Electricity in Grade-7, Reference Note


Electricity simply means the flow of electric charges. When a plastic scale is brought near the piece of paper, it does not attract the paper. But when the scale is rubbed in our hair and brought near the piece of paper, the paper gets attracted to it. At first, the paper was not attracted because the scale was electrically neutral. The number of protons was equal to the number of electron in it. But when we rubbed the scale in our hair, the flow of electrons starts and the comb becomes electrically charged. It is because electrons flow from our hair to the scale and it becomes negatively charged. When the negatively charged scale is brought near the paper, the positive charges of the paper get deposited near the scale. So the papers are attracted in the second stage as the opposite charges attract and similar charges repel each other.

The electricity thus developed in a scale is one of the examples of static electricity. Static electricity is a type of electricity produced due to the friction between two surfaces like hair and plastic comb. Clothes stuck to one another after being in the dryer is another example of static electricity

Causes of Static Electricity

Every material is made of atoms. They contain an equal number of protons (positive charges) and electrons (negative charges) . They are electrically neutral. When electrically neutral materials are in contact, the electrons may transfer from one material to another material causing an excess of positive charges on one material and an equal negative charge on another. When they are separated, they retain their charge imbalance. To cause static electricity, there should be the separation of positive and negative charges.

Body charged by Friction

As we know that every substance is electrically neutral. They are made of atoms. They have an equal number of protons and neutrons. Protons are positively charged and electrons are negatively charged. The protons are present in the nucleus of an atom whereas the electrons revolve around it. It is very hard to transfer the proton from one material to another material because they are strongly held by the nucleus. But the electrons are loosely held. When we rub two bodies, heat energy is developed due to the friction which is responsible for the movement of electrons from one body to another body. The body which gains an electron from another body is negatively charged due to the high concentration of electrons in it than the concentration of protons. The substance which gives out electrons to another body is called negatively charged body as there is an excess of protons or greater number of protons than the number of electrons present in it. So we can also say that the body with a high concentration of electrons than protons is negatively charged and the body with a high concentration of proton than an electron is positively charged. Charge are developed due to friction in various materials like plastic, wool, polyester, acrylic etc.

Effects of Static electricity

We can see various effects of static electricity around us in our environment. One of the most common and popular examples of static electricity are lightning and thunderstorm. We can see, feel and hear the lightning and thunderstorm. Lightning is a bright flash of electricity in clouds produced by the thunderstorm. It is the discharge of static electricity between the electrically charged regions within the clouds or between a cloud and the surface of the earth. The charged region in the atmosphere equalises them by a lightning flash. There are usually three types of lightning. First, lightning between cloud, second, lightning from cloud to the ground and third, lightning from the cloud itself.Lightning occurs along with the sound of thunder. We can hear the sound if the lightning occurs near our place but we cannot hear the sound of thunder if the lightning occurs far away from our place. But we can clearly see the flash of lightning.
When warm air is mixed with cold air masses, there is a disturbance in atmosphere necessary for polarising the atmosphere. Here, the positively charged air masses moves upward within the clouds and negatively charged air masses moves towards the earth. When there is a transfer of electrons from negatively charged cloud to the positively charged cloud, a large amount of heat is produced. This causes a white flash in the sky making its surrounding air white hot. The hot air moves towards the path of electricity in the form of a wave. This hot air contracts with the electricity in the form of a wave which produces sound. This sound is the sound, that we hear after lightning.


A thunderstorm is also known as an electrical storm, lightning storm or thundershower. It is very dangerous. It produces lightning, strong winds, heavy rainfalls and sometimes hails too. Thunderstorm mainly occurs during spring and summer, especially in afternoon and evening hours. It is also one of the dangerous natural disasters that cause huge loss of life and properties. It also kills animals, destroys forest etc. Sometimes it also causes a fire. In a thunderstorm, the clouds are electrically charged. It was first proved by an American scientist Benjamin Franklin. During the thunderstorm, clouds gather with each other. There occurs very heavy flow of charges between them. This results in the release of a large amount of energy in the form of light, heat, and sound.

Lightning Conductor

A lightning rod is a pointed metal rod attached to the roof of a building to prevent the damage caused by lightning. It is a tall metal rod made of copper or iron with a number of sharp pointed long rods at the top end. It's lower end is connected with the metallic plate that is buried in the ground. As we know that lightning gives out electrical charges, during the rainy season the roof of the house are wet that are capable of conducting heat and electricity. When the lightning passes through this roofs, it can conduct the electricity which can cause loss of life and properties. But when the lightning passes through the roofs fitted with the lightning conductor, the charge is induced on the pointed tips of the conductor. When the lightning strikes on the rod, the charge is conducted down into the earth through a thick metallic rod. Like this, the building is saved from the damages caused by the lightning.