Basic Electricity and Electronic Components
What the exam tests
Basic Electricity and Electronic Components tests your ability to apply Ohm's law and Kirchhoff's laws to DC networks, read resistor and capacitor markings, and choose components whose ratings survive the circuit. Expect numerical questions on series/parallel resistance, power, and simple voltage dividers.
Core rules
- Ohm's law: V=IR; power P=VI=I²R=V²/R. A resistor's power rating must exceed calculated dissipation.
- Series: same current; resistances add; voltage divides in proportion to resistance.
- Parallel: same voltage; conductances add; two-branch formula R=(R1R2)/(R1+R2).
- KCL: sum of currents into a node equals sum out. KVL: algebraic sum of voltages around a loop is zero.
- Resistor colour code: first two bands digits, third multiplier, fourth tolerance (gold ±5%, silver ±10%). A 220Ω ±5% resistor is red-red-brown-gold.
- Capacitors: C=Q/V; series capacitors combine like parallel resistors; electrolytics are polarised.
Worked example
A 12 V supply feeds 220Ω and 330Ω in series. Total R=550Ω, so I=12/550=21.8 mA. Voltage across 330Ω is IR=0.0218×330=7.2 V; across 220Ω it is 4.8 V. Check: 7.2+4.8=12 V. The 220Ω resistor dissipates I²R=(0.0218)²×220=0.105 W, so a 0.25 W part is adequate but a 0.125 W part is marginal.
Traps that cost marks
Mixing rms and peak values in power calculations; forgetting tolerance when stating a colour code; assuming a capacitor blocks DC only after it is charged; and adding parallel resistors directly. In parallel, the equivalent resistance is always smaller than the smallest branch.