1.2. ELECTRIC CHARGE

Historically the credit of discovery of the fact that amber rubbed with wool or silk cloth attracts light objects goes to Thales of Miletus, Greece, around 600 BC. The name electricity is coined from the Greek word 'elektron' meaning amber.

Thales of Miletus, an ancient Greek philosopher, discovered that rubbing amber with materials like wool or silk could attract small objects. This effect led to the foundational concept of electricity, from the Greek word 'elektron' which means amber. This discovery is seen as the beginning of our understanding of electric charge.

Imagine rubbing a balloon on your hair and then being able to stick it to a wall. Just like Thales discovered with amber, the balloon’s ability to attract hair or paper after being rubbed shows the principles of static electricity in action.

There are only two kinds of an entry which is called the electric charge. We say that the bodies like glass or plastic rods, silk, fur, and pith balls are electrified. There are two kinds of electrification: (i) like charges repel and (ii) unlike charges attract each other. The property which differentiates the two kinds of charges is called the polarity of charge.

Electric charge comes in two types: positive and negative. A fundamental characteristic of these charges is that similar charges (like charges) repel each other, while opposite charges (unlike charges) attract each other. This relationship defines the polarity of electric charges and forms the basis for many electrostatic interactions, such as how a charged balloon can stick to a neutral wall.

Consider a fun scenario: you can think of the positive and negative charges like two people with magnets on their backs. If they have magnets that repel each other, they will push away. However, if one person has a positive magnet and the other a negative magnet, they will be drawn together and 'stick'!

When a glass rod is rubbed with silk, the rod acquires one kind of charge and the silk acquires the second kind of charge. If the electrified glass rod is brought in contact with silk, they no longer attract each other. The charges acquired after rubbing are lost when the charged bodies are brought in contact.

When you rub a glass rod with silk, electrons are transferred from the rod to the silk, leading to the rod becoming positively charged and the silk negatively charged. If these two items touch, they neutralize each other; the charges cancel out, which is why they lose their ability to attract or repel.

It’s like having two friends play with a piece of candy. When they share, one friend might end up with no candy (no charge) while the other has all of it, making them both happy when they separate again. But if they touch hands (contact), they evenly distribute the candy and might each end up with an equal piece — leading them to no longer enjoy the candy alone.

The charges were named as positive and negative by the American scientist Benjamin Franklin. By convention, the charge on glass rod or cat’s fur is called positive and that on plastic rod or silk is termed negative.

Benjamin Franklin established the positive and negative naming convention for electric charges. This classification helps us understand and predict how different materials will interact electrically. For example, the charge transferred from glass when rubbed with silk is termed positive, while the charge on silk itself is considered negative.

Think about how kids often sort their toys into 'like' and 'not like' piles. Franklin’s simplification helped people understand that not only can things attract each other if they are different, but also that things can push away if they are the same, just like the similar toy piles being pushed apart!

A simple apparatus to detect charge on a body is the gold-leaf electroscope. It consists of a vertical metal rod housed in a box, with two thin gold leaves attached to its bottom end.

The gold-leaf electroscope is an instrument used to detect electric charges. When a charged object is brought close enough to the metal rod, the charge gets transferred to the gold leaves causing them to diverge. This movement is an indication of the presence of an electric charge, based on the principles of attraction and repulsion between like and unlike charges.

Imagine using a puppet with strings. When you pull on certain strings (bringing a charger close), the puppet's arms move (gold leaves diverge). The stronger you pull, the more dramatic the change — in this case, it’s how we detect if something is charged!

To electrify a neutral body, we need to add or remove one kind of charge. When we say that a body is charged, we always refer to this excess charge or deficit of charge.

Electrifying a neutral object involves either adding electrons (to create a negative charge) or removing them (to create a positive charge). This is essential in understanding how charges are conserved; while charges can be transferred, they cannot be created or destroyed. Hence, the total charge in an isolated system remains constant.

This process can be likened to refilling or draining water from a tank. You can’t create or destroy water, but you can move it from one tank to another, just as you can move charges to create different states of electrification.

--