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+---- Thread: Electricity, Circuits & Electrons — The Foundations of All Electronics (/showthread.php?tid=356)
Electricity, Circuits & Electrons — The Foundations of All Electronics - Leejohnston - 11-17-2025
Thread 1 — Electricity, Circuits & Electrons
The Foundations of Modern Electronic Systems
Electrical engineering begins with the most fundamental concept:
how electric charge moves, interacts, and creates the behaviour of circuits.
This thread builds the foundation every engineer needs before exploring components, systems, and advanced electronics.
1. What Is Electricity?
Electricity is the movement or presence of electric charge.
Key forms:
• electric charge (fundamental property)
• electric current (flow of charge)
• voltage (energy per charge)
• electric fields (forces acting on charges)
Electricity powers:
• electronics
• computing
• communication systems
• lighting
• motors
• sensors
• robotics
2. Voltage, Current & Resistance (V = IR)
Ohm’s Law is the simplest and most important rule in circuits:
V = I × R
Where:
• V = voltage
• I = current
• R = resistance
Analogies:
• voltage = pressure
• current = flow rate
• resistance = pipe restriction
If voltage increases → current increases.
If resistance increases → current decreases.
3. Electric Current — Flow of Charges
Current is measured in amperes (A).
Types:
• DC (direct current): constant direction
• AC (alternating current): periodically reverses
Examples:
• batteries → DC
• household mains → AC
• microchips → DC internally
4. Voltage — Electrical Potential Energy
Voltage is the energy difference that pushes electrons.
Examples:
• a 9V battery
• a 230V mains outlet
• a USB port (5V)
• lithium-ion cells (3.7V)
Higher voltage = more “push” available.
5. Resistance & Conductivity
Resistance limits the flow of current.
Materials:
• conductors = low resistance (copper, aluminium)
• insulators = very high resistance (plastic, rubber)
• semiconductors = controlled resistance (silicon → used in chips)
Resistors convert electrical energy into heat.
6. Power in Circuits (P = VI)
Electrical power is the rate energy is used:
P = V × I
Examples:
• phone charger: 5V × 2A = 10W
• laptop: ~65W
• kettle: 2000–3000W
Power tells us how much energy a device consumes.
7. Series vs Parallel Circuits
Series circuits:
• current is the same through all components
• voltage divides
• if one fails → the whole circuit stops
Example: old Christmas lights.
Parallel circuits:
• voltage is same across all branches
• current divides
• components operate independently
Example: household wiring.
8. Circuit Symbols (Essential Engineering Notation)
Common symbols:
• resistor — zigzag line
• battery — long & short lines
• capacitor — two parallel plates
• inductor — coiled line
• LED — diode + arrows
• switch — break in line
• ground — symbol pointing downward
Engineers communicate using circuit diagrams, not drawings of real components.
9. Kirchhoff’s Circuit Laws
These two rules allow engineers to analyse any circuit.
KCL — Current Law:
Sum of currents entering a node = sum leaving.
KVL — Voltage Law:
Sum of voltages around a loop = 0.
These laws make it possible to calculate unknown voltages and currents.
10. What Comes Next?
This thread is the foundation for the next topics:
• capacitors
• inductors
• diodes
• transistors
• op-amps
• digital logic
• microcontrollers
• PCB design
• signal processing
• power electronics
Electrical engineering builds layer by layer — and this is the first step.
End of Thread — Foundations of Electricity & Circuits