✨ Key Concepts Overview
🔋 Charge & Current – How electrons flow and create electric current
⚡ Potential Difference – The energy each charge carries
🚧 Resistance – Opposition to current flow
📊 Power & Energy – How quickly devices use electrical energy
🔀 DC vs AC – Different types of current flow
🔍 Conductors & Insulators – Materials that allow or block current
1. Electric Charge: The Foundation
Positive and Negative Charges
All matter is made from atoms. Inside every atom, you'll find two types of charged particles:
- Protons – positively charged, held in the nucleus
- Electrons – negatively charged, orbiting in shells around the nucleus
- Neutrons – neutral (no charge), also in the nucleus
Think of it like this: Imagine a balanced weight. In a normal atom, the positive force of protons exactly equals the negative force of electrons, so the overall charge is zero. But if you remove or add electrons, you upset the balance—like a seesaw tipping to one side.
Attraction and Repulsion
Charges behave like magnets, but with a twist:
What this means: A positive charge will pull a negative charge towards it (attraction), but two positive charges will push each other away (repulsion). This fundamental rule governs all electrical behaviour.
Electric Charge (Q): Measured in coulombs (C). A measure of how much electrical "stuff" an object has. The more charge, the stronger the electrical forces.
Q1: An electron has a charge of -1. A proton has a charge of +1. What force would exist between them?
2. Demonstrating Electric Charges: Charging by Friction
What Happens When You Rub?
When you rub two insulating materials together (like a plastic rod and a cloth), something remarkable happens: electrons transfer from one material to the other. This creates a net charge on both objects.
📚 Worked Example: Rubbing a Polythene Rod
Step 1: What happens?
Rub a polythene rod with a cloth for several seconds.
Step 2: Electron transfer
Electrons move from the cloth → into the polythene rod.
Step 3: Result
Polythene rod: Gains electrons = becomes negatively charged
Cloth: Loses electrons = becomes positively charged
Step 4: Behaviour
The rod and cloth now attract each other because they have opposite charges.
Water analogy: Think of electrons like water. If you pour water from one bucket into another, the first bucket loses water and the second gains it. Neither bucket has "extra water" to begin with—it just moves from one place to another. Same with electrons.
The Gold-Leaf Electroscope: Detecting Charge
An electroscope is a simple device that detects whether something is charged. Inside, there's a thin gold leaf hanging from a metal rod. When you touch the metal plate with a charged object, the charge spreads down the rod to the gold leaf. Since both the rod and leaf now have the same charge, they repel each other, and the leaf springs away from the rod.
Key insight: