Basic Electronics and Electrical Fundamentals
The Basic Electronics and Electrical Fundamentals domain checks that you can read a circuit, apply Ohm's law and power formulas, and use a multimeter correctly. Expect numerical questions and questions about component behaviour.
Core quantities
- Ohm's law V = I x R; power P = V x I = I²R. Series resistances add; parallel resistances give a value smaller than the smallest branch.
- A phone battery is about 3.7-3.8 V nominal and 4.2-4.35 V at full charge; the charger supplies 5 V, or more with USB-PD, and the charging IC converts it.
Components and behaviour
- Resistors limit current and set bias; capacitors block DC, pass AC and store charge, so discharge them before an in-circuit resistance test.
- A silicon diode drops about 0.6-0.7 V forward, a Schottky 0.2-0.3 V. A transistor or MOSFET works as a switch; the control terminal drives the load path.
- An inductor opposes change of current and appears mainly in switch-mode supplies.
Measuring
- Volts: probes in parallel, circuit powered. Amps: meter in series, circuit broken. Ohms, continuity and diode mode: circuit dead and, ideally, the component out of circuit.
Worked example
A 3.7 V, 2000 mAh battery stores 3.7 x 2 = 7.4 Wh. A 5 V 2 A charger gives 10 W. Ideal charge time = 7.4 / 10 = 0.74 h. With 80 percent conversion efficiency it is 0.74 / 0.8 = about 0.93 h, and real charging takes longer because the final CV stage tapers current. Reasoning: convert mAh to Wh using battery voltage, then divide by usable power.
Traps that cost marks
- Measuring resistance on a live board and reading parallel paths.
- Confusing 20 mA with 20 A.
- Assuming a capacitor is faulty because it reads low resistance in circuit.
- Forgetting that a 4.2 V rail needs a divider before a 1.8 V ADC.