Static Electricity

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Have you ever wondered what causes a bad hair day or the sparks from your woollen blanket during winter or the random shocks you get from random objects now and then or the standing fur of your pet cat or the most obvious, disastrous lightning dashing across the evening sky!? There can be one answer to all these – Static electricity!!!

The general definition of static electricity is that it is an imbalance of electric charges in a material. The material remains charged until it can discharge these charge (electric current) trough any medium.

Static electricity effects are evidently annoying. However, it should be said that life is impossible without the forces associated with static electricity. Static forces, both positive and negative, hold the world of atoms and molecules together in the right balance. But, what is static electricity? Is it really harmful? Why it is more during winter? To understand the nature of static electricity, one should know what things around are made of.

Atomic Structure
We know that all material objects are composed of atoms (elements). These elements combine to form compounds (molecules). Protons, neutrons and electrons constitute the sub-atomic particles. The massive (comparatively) protons (positively charged) and neutrons (neutral in charge) are located at the centre (nucleus) of the atoms which forms a dense positive core, while ‘electron shells’ which are concentric spherical regions with distinct energy levels are the home of the negatively charged, mass-less electrons.

Electrons are loosely bound in the atoms while protons and neutrons are tightly bound inside the nucleus. A charged atom: A neutral atom has equal number of protons and electrons: i.e., equal number of positive and negative charges. Provided with sufficient energy, electrons can be freed from its attraction to the nucleus, thus removing them from the atom. Electrons from different atoms can enter into the electron shells of an atom. This entering or leaving of electrons makes an atom charged due to the imbalance of positive and negative charges in it. This charged atom is referred to as ion. Ions can be positive (cation) or negative (anion) depending on electrons leaving or entering an atom.

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Formation of cation and anion from a neutral atom by loosing and gaining electron(s) respectively

Transfer of charge
What happens when we have a charged object? Every charged object tends to redistribute the excess charge across its surface by electron movement. This movement of electrons can take place freely only in the case of a conducting body. When a conducting body is charged from a point, the body will distribute the charges across its entire surface.

Additional charged transferred to a conductor getting evenly distributed across its surface of the conductor

Additional charges transferred to a conductor getting evenly distributed across the surface of the conductor

This redistribution of charges can be explained by the basics of charge interaction: unlike charges attract and like charges repel, thus making the excess charges spread across the entire surface away from each other. It should be stressed that additional charges, positive or negative, is redistributed only through the movement of electrons. While additional negative charges (excess of electrons) get distributed by the movement of electrons itself, additional positive charges (deficiency of electrons) attract electrons from elsewhere creating positive charges wherever the electrons have come from.

Like charges attract and unlike charges repel

Like charges repel and unlike charges attract

Conducting human body
We know that human body is a good conductor of electricity. When charges are transferred human body, they spread across the entire body even through the strands of hair. When the hair gets charged (like charges), they repel each other making them rise upward and outward separated from each other as possible. This is the common ‘hair-rising’ phenomenon of static electricity.

Why static electricity effects more during winter?
Shocks from door knobs, bad hair days, etc. are frequent during winter compared to summer. Why? This has to do with the humidity which affects static charges. Water molecules can remove the extra charges in a material. We often fix our hair with water! Winter is the driest of all seasons with little moisture in air and the static charges remain more on the surfaces of the body often getting discharged via static electricity.

Polarization of charges
We know that like charges attract each over and unlike charges repel each other. But what about the interaction between a charged and neutral particle? There is always an attractive force between a charged (positive or negative) and neutral particles. This is due to the polarization of charges in a material. Polarization is the process of separation of charges within a material; i.e., the positive and negative charges get separated forming two poles at either ends as shown in the following image:

Polarisation of charges

Polarisation of charges

Consider the classic example of a charged balloon held against the flowing water from a tap;  the stream of water gets attracted towards the charged balloon. In the vicinity of the charged object (negatively charged balloon), the neutral water molecules will get polarized: Hydrogen as the positive pole and oxygen as the negative pole. Molecules in a liquid are free to move. Hence, the water molecules get realigned and the positively charged oxygen molecules move towards the negatively charged balloon, pulling the entire steam of water with it thereby deflecting its flow.

Polarisation of charges in water causing a deflection of water stream

Polarisation of charges in water causing a deflection of water stream

Charging of objects
So far we have discussed the effects of static charges and charge interactions. Now, let us look into how these charges are created in objects. Charging can be done via various methods such as conduction, induction, friction, etc.

The word conduction  means two objects in contact. Charging by conduction takes place when a charged object is brought in contact with a neutral object, transferring the charges from the charged to the neutral object.

Charging by conduction

Charging by conduction

Charging by induction takes place when the charged object is brought in the vicinity of the neutral object (no contact). This causes a polarization of charges in the neutral object and with proper earthing, one can remove one type of charge from it making it charged.

Charging by induction

Charging by induction

Charging by friction  is the simplest way of charging objects. This is done by rubbing the objects together. As objects of different materials are rubbed together, electrons with weaker bonds (in least electron loving material) are removed from one material and migrate to the other material making both materials charged. Friction is usually the reason behind the static charges getting accumulated on our woollen clothes (when rubbed against us), cat’s fur (when they move about the carpets and us), the balloons (when rubbed against other substance), and so on.

When a glass rod is rubbed on a silk cloth, the glass rod loses electrons to sink, making the silk cloth negatively charges and the glass rod positively charged

When a glass rod is rubbed on a silk cloth, the glass rod loses electrons to sink, making the silk cloth negatively charges and the glass rod positively charged

Lightning
Lightning is one of the dangerous effects of static electricity. It is the discharge of the static charge built up in the clouds. There is a polarization of charges in the clouds; the top parts acquire positive charges while the bottom parts acquire negative charges. This static charging of the clouds is believed to be due to frictional charging.

Frictional charging of clouds
Clouds contain millions of ice particles and water particles suspended in them. When additional water from the ground gets evaporated and rises up forming droplets on its way up towards the cloud, the upward motion of moisture collides (frictional) with the water droplets already suspended in the cloud. During these collisions, electrons are ripped off from the rising droplets causing the bottom of clouds to be negatively charged  and the positively charged droplets rises up to the top of the clouds making the region positively charged..

Lightning strike
The polarization of charges in the cloud, with the electrons gravitating towards the Earth’s surface causes the Earth’s surface to be charged positive. As the build up static charge in clouds increases, there is an increased electric field in the atmosphere surrounding the cloud making it highly conductive. This makes way for an easy path for the transfer of charges from the clouds to the surface of Earth. Since Earth’s atmosphere has numerous dust particles and other impurities, there wont be a straight line transfer of charges from the cloud to the Earth: The reason behind the zig-zag motion and branching in a lightning. Also, the purplish glow of the lightning is a characteristic of the ionized air molecules.

Lightning

Lightning

Lightning is not a discharge from the cloud to the Earth. It can be between cloud to cloud or even within a cloud because of the polarization of charges in the clouds.

Various kinds of discharge from clouds

Various kinds of discharge from clouds

Thunder
The sudden discharge from the clouds heats up the surrounding air which expands violently. This creates a shock wave which we hear as thunder.

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