1. Understanding Electric Charge
Electric charge is a basic property of matter that causes it to experience a force when placed near other charges. Some particles carry positive charge and some carry negative charge. This property exists naturally and does not need to be created from outside.
Every object around us has countless charges inside it, mainly in the form of protons (positive) and electrons (negative). Usually they balance each other, so the object appears neutral.
1.1. Positive and Negative Charges
There are two kinds of electric charges: positive and negative. Like charges repel each other and unlike charges attract. This simple rule helps explain many electrical effects around us.
For example, when a glass rod is rubbed with silk, it becomes positively charged. When a plastic scale is rubbed with hair, it usually becomes negatively charged. This happens because electrons shift from one surface to another.
1.2. Quantisation of Charge
Electric charge is not continuous. It exists in small packets. The smallest possible charge is the charge of an electron.
The amount of charge is always an integer multiple of this smallest charge:
\( q = n e \)
Here, e is the charge of an electron and n is any integer. This is called quantisation of charge.
1.2.1. Meaning of Quantisation
Quantisation simply means you can never have a charge like \( 2.5e \); it must be an exact multiple such as \( 1e, 2e, 5e \), and so on.
2. How Charges Interact
Charges exert forces on each other. This interaction is the reason we see effects like attraction, repulsion and even sparks. When two charged bodies are brought close, they either pull or push each other depending on whether the charges are alike or opposite.
2.1. Simple Observation
If two objects both gain electrons, they become negatively charged and repel. If one object gains electrons and the other loses electrons, they attract. These interactions happen without the objects touching each other because the force acts through the electric field.
3. Conservation of Charge
Conservation of charge means that charge can never be created or destroyed. It can only be transferred from one body to another. The total charge in an isolated system stays constant.
This principle holds for every electrical process, whether it is rubbing objects, charging by contact, charging by induction or current flowing in a circuit.
3.1. What Actually Happens When Two Objects Are Charged?
When one object becomes positively charged, it is simply losing some electrons. Another object gains those electrons and becomes negatively charged. No charge is created out of nothing.
3.1.1. Example to Visualise Conservation
Suppose an object loses \( 3e \). Another must gain exactly \( 3e \). So the total charge before and after remains the same. This is the essence of conservation of charge.
4. Charging and Discharging
Objects become charged when electrons move from one place to another. They become discharged when electrons return or redistribute. Processes like conduction, induction and rubbing are simply ways by which electrons shift around.
Even during a spark or lightning, charges are not created; they are only moved suddenly from one region to another.
5. Key Takeaway
Electric charge is a natural property of matter. It exists in two types, follows simple interaction rules and always remains conserved. All electrical phenomena are ultimately the result of how charges move, rearrange or interact.