Passive Components and Semiconductor Devices
What this domain tests
Passive Components and Semiconductor Devices tests identification, ratings, testing, and application of resistors, capacitors, inductors, transformers, diodes, rectifiers, BJTs, FETs, and optoelectronic devices.
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; third band is multiplier, fourth is tolerance (gold ±5%, silver ±10%).
- Capacitor code: first two digits are significant, third is multiplier in pF; 104 = 10×10^4 pF = 100,000 pF = 100 nF = 0.1 µF.
- Electrolytic capacitors are polarized; reverse voltage damages them.
- Diode: forward drop about 0.7 V for silicon, about 0.3 V for germanium; check with the DMM diode test.
- BJT: base-emitter about 0.6–0.7 V forward; collector-emitter should not be shorted. FET gate is high impedance; handle with ESD care.
Worked example
A four-band resistor reads yellow, violet, red, gold. Yellow=4, violet=7, red multiplier=100, so 47×100=4,700 Ω = 4.7 kΩ, tolerance ±5%, giving 4,465–4,935 Ω. An in-circuit measurement gives 3.2 kΩ. That is suspect, but a parallel path can lower the reading, so lift one end before condemning the resistor.
Traps
Reading a resistor from the wrong end can reverse the digits. Confusing the third band multiplier with the tolerance band is common. Do not treat 104 as 104 pF. A diode that reads high both ways may be open, but compare with a known-good device. Touching FET gates can destroy them. Capacitors may hold charge after power-off.