Passive Components: Resistors, Capacitors and Inductors
Passive components store or dissipate energy and do not amplify. The exam tests types, the resistor colour code, practical testing, and typical applications.
Core facts
- Resistors: carbon film, metal film, wirewound, and potentiometers. They limit current, divide voltage, and set bias.
- Capacitors: ceramic and film are non-polar; electrolytic is polar. They block DC, pass AC, filter, and couple signals. Capacitor code 104 means 10 × 10⁴ pF = 100 nF.
- Inductors: air-core and ferrite-core. They oppose changing current, filter, and tune circuits.
- Colour code digits: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. Gold tolerance ±5%, silver ±10%.
Worked example
A four-band resistor reads brown, black, red, gold. Brown = 1, black = 0, so the significant digits are 10. Red multiplier = ×100, giving 10 × 100 = 1000 Ω = 1 kΩ. Gold means ±5%, so the acceptable range is 950 Ω to 1050 Ω. A meter reading of 970 Ω is therefore within tolerance. To test, isolate the resistor from the circuit and use the ohmmeter range above the expected value.
Traps
- Reading the bands from the tolerance end; start at the band nearest the end.
- Treating gold as a multiplier in a four-band code; it is the tolerance band there.
- Testing a resistor while it is still connected, so parallel paths give a false low reading.
- Connecting an electrolytic capacitor with reversed polarity.