Basic Electronics: Voltage, Current, Resistance, Capacitance, and Inductance

Electronics is built on a few fundamental concepts and components. Understanding voltage, current, resistance, capacitance, and inductance is essential for working with circuits, from simple LED blinkers to complex computers. These principles govern how electricity behaves in both analog and digital systems.

Voltage (V)

Voltage is the electrical potential difference between two points—the "pressure" that pushes electric charge through a circuit. Measured in volts (V).

Analogy: Like water pressure in a pipe.
Positive voltage means one point has higher potential than another.
Sources: Batteries (DC), wall outlets (AC), power supplies.
Common values: 1.5V (AA battery), 5V (USB/TTL logic), 12V (car battery), 120V/240V (household AC).

Current (I)

Current is the flow of electric charge (electrons) through a conductor. Measured in amperes (A), often milliamps (mA) in small circuits.

Analogy: Like water flow rate in a pipe.
Conventional current flows from positive to negative (opposite to electron flow).
Too much current can overheat components or wires.

Resistance (R)

Resistance opposes the flow of current. Measured in ohms (O).

Analogy: Like friction or a narrow section in a pipe.
Materials: Conductors (low R, e.g., copper), insulators (high R, e.g., rubber).
Resistors are components with fixed or variable resistance.

Ohm's Law

The fundamental relationship: V = I × R (Voltage = Current × Resistance)

Rearranged: I = V / R, R = V / I
Example: 5V across a 1000O resistor ? I = 5 / 1000 = 0.005A = 5mA

Capacitance (C)

Capacitance is the ability to store electric charge. Measured in farads (F), usually microfarads (µF), nanofarads (nF), or picofarads (pF).

Component: Capacitor—two plates separated by an insulator.
Behavior: Blocks DC, passes AC; charges/discharges over time.
Uses: Filtering noise, timing circuits (with resistors), energy storage, decoupling power supplies.
Time constant: t = R × C (time to charge/discharge ~63%).

Inductance (L)

Inductance is the ability to store energy in a magnetic field when current flows. Measured in henries (H), usually millihenries (mH) or microhenries (µH).

Component: Inductor (coil of wire).
Behavior: Opposes changes in current; generates voltage when current changes.
Uses: Filtering, energy storage in switching supplies, transformers, radio tuning.
Time constant: t = L / R (in RL circuits).

Power (P)

Power is the rate of energy transfer. Measured in watts (W).

P = V × I
Also: P = I² × R or P = V² / R
Example: 5V at 100mA ? P = 0.5W

Summary Table

Quantity	Symbol	Unit	Analogy	Key Formula
Voltage	V	Volts (V)	Pressure	V = I × R
Current	I	Amps (A)	Flow rate	I = V / R
Resistance	R	Ohms (O)	Friction	R = V / I
Capacitance	C	Farads (F)	Bucket size	Q = C × V
Inductance	L	Henries (H)	Inertia	V = L × dI/dt
Power	P	Watts (W)	Work rate	P = V × I

Why It Matters

These concepts explain how every electronic device works—from the power supply in a vintage computer to the timing circuits in early microprocessors. Mastering them enables reading schematics, troubleshooting circuits, and understanding the physical layer beneath digital logic.

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