Electronic Components and Devices
What this domain tests
Electronic Components and Devices tests identification, ratings, polarity and basic testing of resistors, capacitors, inductors, diodes, LEDs, transistors and simple switches. Expect colour-code, capacitor-code and pinout questions.
Core rules
- Resistor colour values: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. In a 4-band resistor the first two bands are digits, the third is the multiplier, and the fourth is tolerance: brown ±1%, red ±2%, gold ±5%, silver ±10%.
- Capacitor code 104 means 10 × 10⁴ pF = 100,000 pF = 100 nF = 0.1 µF. Electrolytic capacitors are polarised; the stripe marks negative.
- A diode conducts when anode is positive relative to cathode (forward bias); the band marks cathode. An LED needs a series current-limiting resistor.
- In an NPN transistor the emitter arrow points out; in a PNP it points in. The base controls collector-emitter current.
Worked example
A resistor reads brown, black, red, gold. Digits: 1 and 0, so 10; multiplier red = ×100; value = 10 × 100 = 1,000 Ω = 1 kΩ. Gold tolerance = ±5%, so the acceptable range is 950 Ω to 1,050 Ω. A meter reading of 990 Ω is therefore normal; 1,200 Ω is out of tolerance.
Traps
Reading the colour bands from the wrong end, so the tolerance band is mistaken for a digit; mixing pF, nF and µF by factors of 1,000; assuming a diode conducts in both directions; and using a transistor without checking whether its pin order is E-B-C or C-B-E. LED failure often means the series resistor was omitted.