Three components, three jobs
The foundations track defined capacitance and inductance as properties. Here they are as parts, and the pool asks the same fact from both directions — by function and by construction.
| Component | Function | Construction |
|---|---|---|
| Resistor | opposes the flow of current in a DC circuit | resistive film or wire |
| Capacitor | stores energy in an electric field | conductive surfaces separated by an insulating material |
| Inductor | stores energy in a magnetic field | a coil of wire |
Both directions get asked. “What component stores energy in a magnetic field?” and “What component is typically constructed as a coil of wire?” have the same answer, and knowing why keeps you from having to memorise two facts.
Variable resistors
What type of component is often used as an adjustable volume control?
Potentiometer.
What electrical parameter is controlled by a potentiometer?
Resistance.
A potentiometer is a resistive track with a movable contact. Turning the shaft moves the contact, changing the resistance between it and each end — which is why it works as a volume control, a squelch control, and a bias adjustment.
Note the answer to the second question is resistance, not voltage. A potentiometer used as a divider produces a variable voltage, but the parameter the component itself controls is resistance.
Switches
Switch names describe two things: how many independent circuits are switched (poles) and how many positions each can select (throws).
- SPST — single-pole single-throw. One circuit, on or off.
- SPDT — single-pole double-throw. A single circuit is switched between one of two other circuits.
- DPDT — double-pole double-throw. Two circuits, each switched between two destinations.
An antenna changeover switch is SPDT: one antenna feed, selected between two radios. A power switch is SPST.
Batteries
Which of the following battery chemistries is rechargeable?
All these choices are correct — nickel-metal hydride, lithium-ion, and lead-acid.
Which of the following battery chemistries is not rechargeable?
Carbon-zinc.
Carbon-zinc is the cheap primary cell — and, alongside alkaline, the one that must never go in a charger. Attempting it produces heat, gas, and sometimes a ruptured cell, which is the hazard the safety module covers.
The three rechargeable chemistries each have a personality worth knowing:
- Lead-acid — heavy, cheap, tolerant of high current, vents hydrogen. The station backup battery.
- NiMH — moderate capacity, safe, self-discharges. Handheld packs and AA replacements.
- Lithium-ion — highest energy density, needs protection circuitry, fails energetically when abused. Modern handhelds and portable power stations.
Fuses
A fuse removes power in the event of an overload, protecting the wiring rather than you or the equipment. Never fit a larger one than specified — the safety module explains why in terms of the I²R heating that follows.
Check yourself
- A component is described as “conductive surfaces separated by an insulating material”. What is it, and what does it store energy in?
- You need to switch one antenna between two radios. What switch type?
- Which of lead-acid, carbon-zinc, and lithium-ion must never be charged?
Answers
- A capacitor, storing energy in an electric field.
- SPDT — a single circuit switched between one of two others.
- Carbon-zinc. The other two are rechargeable chemistries.