Basic Electronics and Passive Components
What this domain tests
The Basic Electronics and Passive Components domain checks whether you can read a circuit the way the paper sets it: units and prefixes, resistor colour codes, series and parallel networks, and how capacitors and inductors behave with DC and AC. Questions are usually short numericals plus one reasoning item on tolerance or power rating.
Core rules
- Prefixes: pico 10⁻¹², nano 10⁻⁹, micro 10⁻⁶, milli 10⁻³, kilo 10³, mega 10⁶. So 4.7 kΩ = 4700 Ω and 2.2 µF = 2.2 × 10⁻⁶ F.
- Resistor colour digits: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. The third band is the multiplier; gold means ×0.1 (5%), silver ×0.01 (10%).
- Series resistances add; for parallel, 1/R = 1/R1 + 1/R2, or product over sum for two. Voltage divides in series; current divides in parallel.
- Capacitors: Q = CV, energy = ½CV², reactance Xc = 1/(2πfC). They block DC and pass AC, and series capacitors combine like parallel resistors.
- Inductors: XL = 2πfL; series inductors add when there is no mutual coupling.
Worked example
Bands brown, black, red, gold read as 1, 0, ×100 = 1000 Ω = 1 kΩ with ±5% tolerance, i.e. anything from 950 Ω to 1050 Ω. Two such resistors in parallel give (1 × 1)/(1 + 1) = 0.5 kΩ = 500 Ω. Each carries half the current, but the pair can dissipate twice the power of one at the same voltage.
Traps that cost marks
Reading the code from the tolerance end; writing 1 kΩ as 100 Ω; applying the resistor formula to capacitors; treating a capacitor as an open circuit to AC when its reactance actually falls as frequency rises; ignoring power rating, so a ¼ W resistor is used where 1 W is dissipated.