Basic Electronics
Basic Electronics
This domain covers passive components, their markings, and simple electronic circuits: resistors, capacitors, inductors, transformers, diodes, transistors, rectifiers and filters.
Core rules
- Resistor colour code: Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Grey 8, White 9; gold ±5%, silver ±10%.
- Capacitance in farads; capacitors block DC and pass AC; impedance X_C = 1/(2πfC).
- Inductors oppose changing current; X_L = 2πfL; transformers change AC voltage by turns ratio Np/Ns.
- A diode conducts in forward bias above about 0.7 V for silicon; a transistor amplifies or switches.
- A bridge rectifier with a filter capacitor converts AC to smoother DC.
Worked example
A resistor is marked Brown, Black, Red, Gold. First band 1, second 0, multiplier 10² = 100, so 10 × 100 = 1000 Ω = 1 kΩ; gold means ±5%. The acceptable range is 950 Ω to 1050 Ω. If it reads 1.2 kΩ on a multimeter, it is out of tolerance and should be replaced.
Traps that cost marks
Reading the colour bands from the wrong end; confusing multiplier with tolerance band; using a capacitor's voltage rating as its capacitance; assuming a transformer works on DC; forgetting that a silicon diode has a forward drop.