Electrical and Electronic Fundamentals
Core quantities and relationships
Every question in this domain reduces to charge, current, voltage, resistance and power. Current (I) is the rate of charge flow in amperes; voltage (V) is energy per unit charge; resistance (R) opposes current and dissipates energy as heat. Ohm's law V = IR and the power relationships P = VI = I²R = V²/R are assumed knowledge. In series, currents are equal and voltages add; in parallel, voltages are equal and currents add. Conductance is the reciprocal of resistance.
AC, waveforms and decibels
Alternating waveforms are described by frequency (f), period (T = 1/f), peak, peak-to-peak and RMS values. For a sine wave, RMS = peak/√2 ≈ 0.707 × peak, and average power uses RMS values. Decibels compare power: dB = 10 log10(P2/P1); for voltage or current in equal impedances, dB = 20 log10(V2/V1). Learn the anchors: +3 dB is double power, +10 dB is ten times, −3 dB is half.
Traps and rule of thumb
Questions often mix peak and RMS, or quote peak-to-peak while asking for RMS. Watch prefixes (m = 10⁻³, µ = 10⁻⁶, k = 10³, M = 10⁶) and remember that a 50 Hz waveform has a 20 ms period. Capacitors and inductors store energy rather than dissipate it, so they behave differently from resistors in AC circuits.
Worked example: a 240 V RMS sine has a peak of 240 × 1.414 ≈ 339 V and a peak-to-peak of about 678 V. A 12 V supply across 4 Ω draws 3 A and dissipates 36 W.