Electronic Components and Devices
What this domain tests
Identification, code reading, polarity and basic application of resistors, capacitors, inductors, diodes, LEDs and transistors. Expect colour-code and capacitor-code questions plus a simple LED series-resistor calculation.
Rules
- Four-band resistor: digit, digit, multiplier, tolerance. Black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9; gold ±5%, silver ±10%.
- Capacitor code 104 = 10 × 10⁴ pF = 100,000 pF = 100 nF = 0.1 µF. Electrolytic capacitors are polarised; the stripe marks negative.
- Diode: anode is the triangle side, cathode is the bar. Silicon forward drop ≈ 0.7 V, germanium ≈ 0.3 V. Reverse bias blocks current.
- LED series resistor: R = (V_supply − V_forward)/I.
- Transistor as a switch: base current through a resistor turns on collector current; E = emitter, B = base, C = collector.
- An inductor opposes change in current; its unit is the henry.
Worked example
A red LED with V_f = 2.0 V and I = 20 mA runs from 5 V. R = (5 − 2)/0.02 = 150 Ω. The nearest standard value, 150 Ω, gives exactly 20 mA; 180 Ω gives about 16.7 mA and is safer if brightness is adequate. Resistor power = I²R = 0.02² × 150 = 0.06 W, so a 1/4 W part is fine.
Traps
- Reading a 5-band resistor as 4-band, or starting from the wrong end; the tolerance band is usually spaced away.
- Treating 104 as 104 pF.
- Reversing LED polarity.
- Omitting the base resistor and destroying the transistor.