Basic Electronics and Passive Components
What this domain covers
The Basic Electronics and Passive Components domain tests your ability to identify, read and combine resistors, capacitors and inductors, and to predict how they behave in DC and AC circuits. Questions commonly ask for colour-code values, capacitor markings, series/parallel equivalents, and reactance at a given frequency.
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. In a four-band resistor the first two bands are digits, the third is the multiplier (power of ten) and the fourth is tolerance: gold ±5 %, silver ±10 %, no band ±20 %.
- Capacitor code: the first two digits are significant figures and the third is the multiplier in picofarads. 104 = 10 × 10⁴ pF = 100 nF = 0.1 µF.
- Series/parallel: resistors add in series and use the reciprocal rule in parallel; capacitors do the opposite.
- Reactance: X_C = 1/(2πfC) falls with frequency; X_L = 2πfL rises with frequency.
Worked example
A resistor shows brown, black, red, gold. Digits 1 and 0, multiplier ×100 → 1000 Ω = 1 kΩ, tolerance ±5 %, so the acceptable range is 950 Ω to 1050 Ω. A capacitor marked 473 is 47 × 10³ pF = 47 000 pF = 47 nF.
Traps that cost marks
Reading the bands from the tolerance end; treating the third band as a digit instead of a multiplier; forgetting that capacitor codes are in picofarads, not microfarads; ignoring electrolytic polarity; and mixing the series and parallel rules when capacitors are involved.