⚡ Fast Revision: Static Electricity
Electric Charges
- Types: Positive (Protons) and Negative (Electrons).
- Law of Electrostatics: Like charges repel; unlike charges attract.
- Conservation: Total charge in an isolated system remains constant; charges are only transferred.
- Conductors vs. Insulators: Conductors allow free flow of electrons (Metals); Insulators do not (Rubber, Plastic).
Unit Alert
Electric Charge: Q | SI Unit: Coulomb (C)
Charge of 1 Electron: $1.6 \times 10^{-19}\ C$
| Method of Charging | Process | Final Result |
|---|---|---|
| Friction | Rubbing two insulators together. | Opposite charges produced. |
| Conduction | Direct contact with a charged body. | Same charge produced. |
| Induction | Bringing a charged body near without touching. | Temporary opposite charge. |
❌ Common Error:
Thinking protons move during charging. Fix: Only electrons move. A body becomes positive by losing electrons, not by gaining protons.
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Gold Leaf Electroscope (GLE)
⚡ Fast Revision: Current Electricity
Flow of Charges
- Electric Current: The rate of flow of electric charge through a conductor.
- Potential Difference (V): The work done in moving a unit positive charge from one point to another.
- Resistance (R): The obstruction offered by a conductor to the flow of current.
- Direction: Conventional current flows from Positive to Negative terminal (opposite to electron flow).
Ohm's Law & Current Formulas:
$I = \frac{Q}{t}$
$V = I \times R$
| Quantity | SI Unit | Measuring Instrument |
|---|---|---|
| Current ($I$) | Ampere (A) | Ammeter (Series) |
| Potential Diff ($V$) | Volt (V) | Voltmeter (Parallel) |
| Resistance ($R$) | Ohm ($\Omega$) | Ohmmeter |
❌ Common Error:
Connecting an Ammeter in parallel. Fix: Ammeter has very low resistance and must always be in Series. Voltmeter has high resistance and must be in Parallel.
Standard Circuit Connections
⚡ Fast Revision: Household Electricity & Safety
Domestic Wiring Components
- Live Wire (L): Carries current at high potential (usually Brown/Red).
- Neutral Wire (N): Provides the return path (usually Blue/Black).
- Earth Wire (E): Safety wire that connects the appliance casing to the ground (usually Green/Yellow).
- Parallel Connection: Household appliances are always connected in parallel so that they can operate independently at the same voltage.
| Safety Device | Function | Key Feature |
|---|---|---|
| Electric Fuse | Protects against Short Circuit/Overloading. | Low melting point wire; breaks circuit if current is too high. |
| MCB | Miniature Circuit Breaker (Modern replacement for fuse). | Automatic switch that trips; can be reset easily. |
| Earthing | Prevents electric shocks from metal casings. | Directs leakage current safely to the earth. |
Energy Consumption
Electrical Energy: $E = P \times t$
1 Unit (kWh): Energy consumed by a 1000W appliance in 1 hour.
❌ Common Error:
Connecting the Fuse to the Neutral wire. Fix: The Fuse must always be connected to the Live Wire so that the appliance is disconnected from the high potential when the fuse blows.
Domestic 3-Pin Plug Wiring
End of Electricity Revision