⚡ Fast Revision: Static Electricity & Charges
- Types: Positive (+) and Negative (-). Like charges repel, unlike charges attract.
- Static Electricity: The buildup of electric charge on the surface of an object, usually through friction.
- Electrons: Only electrons (negative charges) move during charging; protons remain fixed in the nucleus.
Friction: Rubbing two insulators together.
Conduction: Charging by physical contact with a charged body.
Induction: Charging without physical contact.
| Material | Description | Examples |
|---|---|---|
| Conductors | Allow electricity to flow easily. | Copper, Iron, Aluminum |
| Insulators | Do not allow flow of electricity. | Rubber, Plastic, Wood |
Thinking a neutral object has no charges. Fix: Neutral means it has an equal number of positive and negative charges, which cancel each other out.
⚡ Fast Revision: Current Electricity & Circuits
- Current (I): The rate of flow of electric charges.
- Conventional Current: Flows from Positive (+) to Negative (-) terminal.
- Electron Flow: Actually flows from Negative (-) to Positive (+) terminal.
$V = I \times R$
Where V is Potential Difference, I is Current, and R is Resistance.
| Component | Symbol Function | SI Unit |
|---|---|---|
| Cell / Battery | Source of energy | Volt (V) |
| Ammeter | Measures Current (Connected in Series) | Ampere (A) |
| Voltmeter | Measures Voltage (Connected in Parallel) | Volt (V) |
Electric Fuse: A safety wire with a low melting point that breaks the circuit during an overload.
MCB (Miniature Circuit Breaker): Modern switch that automatically turns off when current exceeds limit.
Connecting an Ammeter in parallel. Fix: Ammeters have low resistance and must be in series; Voltmeters have high resistance and must be in parallel.
⚡ Fast Revision: Magnetism & Electromagnets
- Magnetic Poles: Every magnet has a North (N) and South (S) pole. Poles always exist in pairs.
- Directive Property: A freely suspended magnet always points in the North-South direction.
- Magnetic Field: The region around a magnet where its force can be detected. Lines flow from N to S outside the magnet.
| Feature | Permanent Magnet | Electromagnet (Temporary) |
|---|---|---|
| Nature | Retains magnetism for a long time. | Magnetic only when current flows. |
| Strength | Fixed strength. | Variable (Adjusted by current/turns). |
| Polarity | Fixed poles. | Reversible by changing current direction. |
Electromagnetism: When electric current passes through a wire, it behaves like a magnet. This is the Magnetic Effect of Electric Current.
Applications: Electric bells, Maglev trains, and MRI machines.
Using a steel core for an electromagnet. Fix: Use a Soft Iron core because it loses magnetism instantly when current is off. Steel would become a permanent magnet.