Basic Electrical and Electronic Fundamentals
This domain tests whether you can reason about voltage, current, resistance, power and the two basic circuit connections. Questions are usually short calculations or circuit-logic checks rather than memory recall.
Core quantities and laws
- Current (I) is the rate of charge flow, measured in amperes (A); 1 A = 1 coulomb/second.
- Voltage (V) is potential difference, measured in volts; it drives current through a circuit.
- Resistance (R) opposes current, measured in ohms (Ω).
- Ohm's law: V = I × R, with consistent units.
- Power: P = V × I = I²R = V²/R.
- Series: one path, same current everywhere, resistances add: R_total = R1 + R2 + ...
- Parallel: same voltage across branches, reciprocal resistances add: 1/R_total = 1/R1 + 1/R2 + ...
- Kirchhoff's laws: current into a node equals current out; voltage rises equal voltage drops around a loop.
Worked example
A 12 V supply feeds 100 Ω and 220 Ω in series. R_total = 320 Ω, so I = 12/320 = 0.0375 A = 37.5 mA. The drop across 100 Ω is 0.0375 × 100 = 3.75 V; across 220 Ω it is 8.25 V. Power in the 220 Ω resistor is I²R = 0.0375² × 220 = 0.309 W, so a 0.5 W part is adequate but a 0.25 W part is not.
Traps that cost marks
Mixing milliamperes with amperes in V = IR; assuming parallel resistors add directly; confusing the voltage across a component with the current through it; forgetting that a series circuit's largest resistor has the largest voltage drop but the same current.
Exam focus
Be ready to convert units, identify series versus parallel from a description, and check whether a calculated power exceeds a component rating.