Basic Electricity and Electronic Components
The Basic Electricity and Electronic Components domain tests DC circuit laws, passive components and component identification. Questions often ask you to calculate current, voltage or power, read a resistor color code, or choose a component rating that will not overheat.
Core rules and concepts
- Ohm’s law: V = IR; power: P = VI = I²R = V²/R.
- Series: same current, resistances add. Parallel: same voltage, 1/R_T = 1/R1 + 1/R2 + …; the equivalent is always less than the smallest branch.
- Four-band resistor code: first two digits, multiplier, tolerance. Brown-black-red-gold = 1, 0 × 100 = 1 kΩ, ±5%.
- Capacitors store energy in farads (F); electrolytics are polarized and need a voltage rating above the circuit voltage. Inductors are rated in henries (H).
- Use SI prefixes correctly: 1 kΩ = 10³ Ω, 1 mA = 10⁻³ A, 1 µF = 10⁻⁶ F.
Worked example
A 220 Ω resistor is connected across a 5 V supply. Find the current and power, and select a rating. I = V/R = 5/220 = 0.0227 A = 22.7 mA. P = VI = 5 × 0.0227 = 0.1136 W ≈ 114 mW. A ¼ W (250 mW) resistor is suitable because it has more than twice the required dissipation; a ⅛ W part would be too close to its limit.
Traps that cost marks
Writing 22.7 mA as 2.27 A; assuming parallel resistors add directly; ignoring resistor tolerance when a precise value is needed; fitting a polarized capacitor backwards; forgetting that power rating is a maximum, not a target.