Basic Electrical Terms
| Term | Meaning | Unit |
|---|---|---|
| Voltage (V) | Electrical pressure that pushes current | Volt (V) |
| Current (I) | Flow of electric charge | Ampere (A) |
| Power (P) | Rate at which electrical energy is used | Watt (W) |
| Resistance (R) | Opposition to current flow | Ohm (Ω) |
| Energy | Electrical power used over time | kWh (Unit) |
Important formulas:
- V = I × R
- P = V × I
- I = P ÷ V
- R = V ÷ I
2. Common Switch Types
- One-way switch – controls one light/load from one location.
- Two-way switch – controls one light from two locations.
- Intermediate switch – used when one light must be controlled from 3 or more locations.
- Push button – works only while the button is pressed.
- Bell push/button – commonly used to operate an electric bell.
- Selector switch – selects between different circuits or functions.
3. Electrical Board Components
- Main switch – controls the main supply.
- MCB – protects the circuit from overload and short circuit.
- RCCB/RCBO – provides protection against leakage/electric shock; exact function depends on the device.
- Busbar – a metal conductor used to distribute electrical supply to multiple circuits.
- Neutral bar – provides a common connection point for neutral conductors.
- Earth bar – common connection point for protective earthing conductors.
4. Staircase Light Wiring
A two-way switch circuit is commonly used for staircase lighting.
Example:
Switch 1 → Light → Switch 2
You can turn the same light ON/OFF from either end of the staircase.
5. Push Button & Bell Button
A push button is generally a momentary switch. When pressed, it changes the circuit state and returns when released, depending on whether it is NO or NC.
- NO (Normally Open): circuit is open until pressed.
- NC (Normally Closed): circuit is closed until pressed.
A bell button is usually an NO momentary push button used to activate an electric bell/chime.
6. Quick MCQs
1. Unit of current is:
A) Volt
B) Ampere ✅
C) Watt
D) Ohm
2. Unit of resistance is:
A) Ampere
B) Volt
C) Ohm ✅
D) Watt
3. MCB protects mainly against:
A) Low voltage
B) Overload and short circuit ✅
C) High temperature only
D) Noise
4. A busbar is used for:
A) Measuring voltage
B) Distributing electrical supply ✅
C) Producing electricity
D) Measuring resistance
5. Which switch is commonly used for staircase lighting?
A) One-way switch
B) Two-way switch ✅
C) Bell push
D) Fuse
6. Power is measured in:
A) Volt
B) Ampere
C) Watt ✅
D) Ohm
7. V = ?
A) I/R
B) I × R ✅
C) P × R
D) P/I
8. A bell button is normally:
A) Two-way
B) Intermediate
C) Momentary push button ✅
D) MCB
9. The symbol Ω represents:
A) Voltage
B) Current
C) Resistance ✅
D) Power
10. P = ?
A) V × I ✅
B) V/R
C) I/R
D) R/I
