Electronic Components: O-Level Electronics module overview of resistors, capacitors, diodes, LEDs and the bipolar transistor

What this module is about

Electronic Components introduces the physical building blocks that every later circuit is made from. Where Basic Circuit Concepts gave you the quantities and laws, this module gives you the parts: the resistor that sets currents and voltages, the capacitor that stores charge, the diode that allows current one way only, the light-emitting diode that turns current into light, and the bipolar transistor whose small base current controls a large collector current. Knowing what each part does, its key numbers and how to size it is the practical heart of the subject.

This overview ties the module together and links to every dot point, each with its own worked answers and practice questions. See the full set at /sg-o-level/electronics/syllabus/electronic-components.

Resistors and the colour code

Resistors and the colour code covers the function of a resistor (to limit current and set voltages), the difference between fixed and variable types, and how to read the four-band colour code. The first two bands give the digits, the third is the multiplier and the fourth is the tolerance, so brown-black-red-gold is $1000\ \Omega$ at plus or minus $5$ percent.

Capacitors and charge storage

Capacitors and charge storage describes the capacitor as two plates that store charge, defines capacitance as charge stored per volt, and gives the relationship $Q = CV$. The capacitor charges and discharges through a resistor over time, which is the idea reused in the analogue time-delay circuits later in the course.

Diodes and rectification

Diodes and rectification treats the diode as a one-way component that conducts in forward bias once the voltage exceeds about $0.7\ \text{V}$ and blocks in reverse. This one-way behaviour is used in half-wave rectification to turn an alternating supply into a direct one, with a capacitor added to smooth the output.

Light-emitting diodes

Light-emitting diodes covers the LED as a diode that emits light when it conducts, its forward voltage of around $2\ \text{V}$, and the essential series resistor that fixes a safe current. Sizing that resistor is a direct application of Ohm's law and is one of the most common calculations in the paper.

The bipolar transistor

The bipolar transistor names the three terminals (base, collector and emitter) and explains the central idea: a small base current controls a much larger collector current, with the collector current roughly equal to the current gain multiplied by the base current. This current-control property is what makes the transistor act as a switch or an amplifier in the modules that follow.

A worked LED resistor calculation

How this module is examined

• Know the key numbers. The diode and LED forward voltages (about $0.7\ \text{V}$ and $2\ \text{V}$) and the colour code digits are recall marks worth securing.
• Apply Ohm's law to size parts. LED series resistors and the voltage dropped across a diode are direct Ohm's law calculations; convert units first.
• Explain the mechanism. Markers reward stating that a small base current controls a larger collector current, and that a diode conducts one way only.

Check your knowledge

Work through the quiz for this module to test the colour code, capacitor and diode behaviour, LED resistor sizing and transistor current control, then review the worked explanations.