Fundamentals of Electricity and Electronics
Why it matters
Almost every troubleshooting question reduces to Ohm’s law, Kirchhoff’s laws, or a component’s behavior. Know the vocabulary cold: charge, current (ampere), voltage (volt, an electromotive force or potential difference), resistance (ohm), conductance, power (watt), energy, capacitance (farad), inductance (henry), impedance, and frequency.
Core concepts to master
- Ohm’s law and power: V = IR; P = VI = I²R = V²/R. Be able to rearrange all three forms.
- Series vs parallel: series resistances add and current is common; parallel resistances add as reciprocals and voltage is common. Two equal resistors in parallel are half the value.
- AC vs DC: RMS vs peak (V_peak = √2 × V_rms for a sine wave), frequency, phase, and impedance (resistance plus reactance).
- Components: resistors, capacitors (block DC, pass AC), inductors (pass DC, block high frequency), diodes (one-way), transistors (switch/amplify), op-amps, transformers, and fuses/breakers as protective devices.
- Semiconductors and logic: PN junctions, rectification, and basic digital states.
- Safety-related electricity: grounding, isolation, leakage current, and why a chassis can become energized.
Traps
Confusing voltage with current (“the voltage flows”); forgetting that an open circuit has full source voltage across the break and zero current; treating RMS and peak as interchangeable; and mixing the parallel formula with the series one.
Rule of thumb
Draw it, label it, then calculate. Sketch the loop, mark knowns, and apply Kirchhoff’s voltage law (sum of drops = source) before touching the calculator. If a measured voltage is missing where you expect it, suspect an open; if current is high and voltage low, suspect a short or a load that is too small.
Worked example
A 12 V source feeds 100 Ω in series with 200 Ω. Total R = 300 Ω; I = V/R = 12/300 = 0.04 A (40 mA); the drop across the 200 Ω resistor is IR = 0.04 × 200 = 8 V. Check: 4 V + 8 V = 12 V.