Electronics

If your focus area is Electronics, Sections I and II of your written paper are about the electronics industry: 10 multiple-choice marks and about 15 marks of short answers (roughly six items, at least one worth 4–6 marks), 25 of the 40 written marks. They test Industry Related Manufacturing Technology for electronics: the components, materials, circuits, tools, manufacturing processes, test equipment, WHS and environmental practices of the industry.

• Components: resistors (colour code, tolerance, power rating), capacitors, diodes and LEDs, transistors, ICs, relays, switches, motors.
• Circuit theory: Ohm's law, power, series and parallel circuits, voltage dividers, RC time constants.
• Sensors and outputs: LDRs, thermistors, piezo devices, microphones; LEDs, buzzers, DC and stepper motors, relays.
• Digital electronics: logic gates and truth tables, microcontrollers, PWM.
• Power supplies: transformer, rectifier, smoothing, regulator; batteries.
• Manufacture: PCB design and etching, through-hole and surface-mount assembly, soldering and desoldering.
• Testing and fault-finding: multimeter, oscilloscope, signal tracing, simulation software.
• WHS and environment: extra-low voltage, burns and fumes, ESD, chemicals, lead-free solder, e-waste.

Expect questions that ask you to calculate (show the formula, substitute with units), interpret a circuit (what each component does), or describe a process such as making a PCB.

Resistors limit current and divide voltage. Four-band colour code: first two bands are digits, the third is the multiplier (number of zeros), the fourth is tolerance (gold ± 5%, silver ± 10%).

Example: brown, black, red, gold = 1, 0, × 100 = 1000 Ω = 1 kΩ ± 5%. Resistors also have a power rating (commonly 0.25 W); the power dissipated must stay below it.

Capacitors store charge. Capacitance is in farads (usually µF, nF or pF). Electrolytic capacitors are polarised (stripe marks the negative lead) and can burst if reversed; ceramic and film capacitors are not polarised. Uses: smoothing, timing, coupling and decoupling.

Diodes conduct in one direction only (about 0.6–0.7 V forward drop for silicon); the band marks the cathode. LEDs emit light when forward biased and need a series resistor. Zener diodes conduct in reverse at a set voltage and are used for simple regulation.

Transistors (NPN, PNP, MOSFET) act as switches or amplifiers: a small base current (or gate voltage for a MOSFET) controls a much larger collector current. Integrated circuits put many components on one chip: smaller, cheaper in volume, more reliable and lower power.

Relays are electromagnetic switches: a small coil current operates contacts in a separate circuit. A diode across the coil absorbs the voltage spike when it switches off.

• Series: same current everywhere; voltages add; $R_T=R_1+R_2+\dots$
• Parallel: same voltage across each branch; currents add; $\frac{1}{R_T}=\frac{1}{R_1}+\frac{1}{R_2}+\dots$ or for two resistors $R_T=\frac{R_1{R}_2}{R_1+R_2}$ The total is always less than the smallest resistor.
• Voltage divider: $V_{out}=V_{in}\times \frac{R_2}{R_1+R_2}$ with $R_2$ the resistor the output is measured across.
• LED resistor: $R=\frac{V_s-V_f}{I}$ (add the forward voltages of LEDs in series).
• Time constant: $\tau =RC$. A capacitor charges to about 63% in one time constant and is effectively full after about $5\tau$.
• Frequency: $f=1÷T$. On an oscilloscope, $T$ = divisions per cycle × time per division.
• Battery life: hours ≈ capacity (mAh) ÷ current (mA).

Worked example: a 680 Ω and a 330 Ω resistor in series across 6 V.

Always convert prefixes: 1 kΩ = 1000 Ω, 1 mA = 0.001 A, 1 µF = 10⁻⁶ F.

• LDR: resistance falls as light increases. NTC thermistor: resistance falls as temperature rises (PTC rises). In a voltage divider, these changes become a changing voltage.
• Piezoelectric devices produce a voltage when stressed and move when a voltage is applied: buzzers, knock and vibration sensors, gas-lighter sparkers, quartz crystals.
• Switches: push buttons, reed switches (operated by a magnet), tilt and microswitches.
• DC motors turn continuously (speed by voltage or PWM); stepper motors move in fixed steps (often 1.8°) so position is known by counting steps, ideal for 3D printers and CNC machines; servo motors use feedback to hold an angle.
• Sensor → processor → output: a typical automatic circuit is a voltage divider with a sensor, a transistor or microcontroller, then an output device. For example, in an LDR night light the fixed resistor is chosen so the base voltage of the transistor stays below about 0.6 V in daylight and rises past it in the dark, switching the transistor and the light on.

Logic gates (1 = HIGH, 0 = LOW):

A NOT gate inverts its single input. Microcontrollers (such as the boards used in school projects) read inputs, run a program and drive outputs. Pulse-width modulation (PWM) switches an output rapidly on and off; the duty cycle (percentage of time on) sets LED brightness or motor speed.

A linear DC supply converts 230 V AC mains in four stages:

1. Transformer: steps the voltage down and isolates the output from the mains.
2. Rectifier: a bridge of four diodes turns AC into pulsing DC.
3. Smoothing capacitor: charges on the peaks and supplies current between them, leaving a small ripple.
4. Regulator: an IC such as a 7805 (5 V) holds the output constant.

Switch-mode supplies (phone chargers, computer supplies) switch at high frequency so they are smaller, lighter and more efficient.

PCB manufacture (photo-etching, school and prototype scale): design the layout in PCB software → print a mask → expose a photoresist-coated copper board to UV light through the mask → develop (remove exposed resist) → etch away unprotected copper (ferric chloride or ammonium persulfate) → strip the resist → drill holes → clean and protect (tinning or lacquer). Industry also uses CNC milling of prototype boards and plated-through holes, multilayer boards and solder mask.

Assembly:

• Through-hole: leads pass through holes and are soldered on the other side, by hand or by wave soldering. Strong joints, easy to prototype and repair.
• Surface mount (SMT): solder paste is printed through a stencil, pick-and-place machines position surface-mount devices (SMDs), and the board passes through a reflow oven. Much smaller, denser, both sides, fully automated.
• Automated optical inspection and in-circuit testing check every board.

Soldering: heat both pad and lead with a clean, tinned iron, feed flux-cored solder into the joint, remove solder then iron, and keep it still. A good joint is smooth, shiny and concave. Flux removes oxides so the solder wets the metals. Faults: dry joints (dull, balled, poor contact), bridges (solder joining tracks) and lifted pads from overheating. Lead-free solders (tin–silver–copper, about 217–220 °C) melt hotter than 63/37 tin–lead (183 °C). Desoldering uses a solder sucker or braid.

• Multimeter: voltage in parallel; current in series (on a current range and socket); resistance and continuity with the circuit off. Check the range and leads before measuring.
• Oscilloscope: shows voltage against time, so you can measure amplitude, period, frequency and see distortion. Use a signal generator to inject a test signal and trace it stage by stage.
• Logic probe: shows HIGH or LOW at a digital test point.
• Simulation software tests circuits virtually before building them. It is fast and cheap but depends on accurate models, so a prototype is still built and tested.
• Fault-finding: visual inspection first (dry joints, bridges, reversed components), then check supply voltage, then trace signals from input to output.

• Electrical safety: school projects use extra-low voltage (no more than 50 V AC or 120 V ripple-free DC, as defined in AS/NZS 3000). Mains wiring work in NSW must be done by a licensed electrician. Portable equipment is inspected, tested and tagged.
• Soldering: burns (iron in its stand, never touch the tip), flux fumes (fume extractor; rosin fumes can cause asthma), lead (lead-free solder, wash hands, no food at the bench), flying lead clippings (safety glasses).
• Chemicals: etchants are corrosive and stain; use gloves and goggles, follow the SDS and dispose of spent etchant as hazardous waste.
• ESD: static can destroy CMOS ICs and MOSFETs; use an earthed wrist strap, mat and anti-static bags.
• Batteries: lithium cells can overheat or catch fire if short-circuited, punctured or overcharged.
• E-waste: contains hazardous substances (lead, mercury, cadmium, flame retardants) and valuable metals (copper, gold, silver). As at 2026, Australia's National Television and Computer Recycling Scheme has industry fund the collection of TVs and computers, and several states (including South Australia and Victoria) ban e-waste from landfill. Industry responses include lead-free components (following the EU's RoHS rules), design for repair and disassembly, and take-back schemes.

• Leaving kΩ, mA or µF unconverted in calculations.
• Using the parallel formula for series resistors (or the reverse), or adding parallel resistances.
• Forgetting to subtract the LED's forward voltage when finding its series resistor.
• Reading the third colour band as a digit instead of a multiplier.
• Connecting an ammeter in parallel.
• Mixing up NAND and NOR, or LDR and thermistor behaviour.
• Saying the transformer converts AC to DC (the rectifier does).
• Describing soldering as 'melting solder onto the iron and dabbing it on'.

• Interpret a circuit: say what each component does and how the signal passes from input to output.
• Describe a process: give the stages in order, with the materials, equipment and safety precautions for each.
• In calculations, write the formula, substitute with units, keep unrounded values, and give the unit asked for.
• Use precise terms ('forward voltage', 'time constant', 'duty cycle', 'reflow soldering', 'signal tracing').

• Industry Study (Section III): use electronics examples such as automated SMT assembly lines, offshore manufacturing and global supply chains, e-waste and product stewardship, RoHS and lead-free manufacture, apprenticeships in electrotechnology, and WHS hazards such as solder fumes and electric shock.
• Major Project: circuit design, simulation, PCB manufacture and testing are evidence for your folio.