Electronic components: name the job, then the part

This topic hands you a property — what a part does to current, what it is built from, or what its terminals are called — and asks which component fits. A second group of questions points at a numbered symbol in one of the pool's schematic figures and asks what that component is, or what it does in that circuit.

Every part is defined by one property

Answer from the property, not from familiarity. Every component here belongs to one of four families — parts that oppose current or divide voltage, parts that store energy, parts that steer or amplify it, and parts that convert, switch or measure it — and inside a family each member is separated from its neighbours by a single property. Find that property in the prompt, settle the family first, then take the member whose defining property matches it exactly.

Switch names are arithmetic rather than vocabulary. A pole is one circuit the switch handles, a throw is one destination a pole can be connected to, so a switch of one pole and one throw merely opens and closes that circuit, a second throw gives it somewhere else to go, and a second pole repeats the whole arrangement on another circuit. Electrode names deserve the same care: they are proper names owned by one device family, and a set of names assembled out of generic circuit roles is describing what the wires do rather than what a device's electrodes are called. Gain follows suit — it is a ratio of output to input, and the number means nothing until it says which quantity is being compared.

Two ideas sit beside the parts list. Resonance is a cancellation: a tuned circuit is one in which two opposite kinds of opposition to alternating current annul each other at a single frequency, so nothing that merely dissipates energy has any part in it. And a schematic is a map: standard symbols joined by lines that state truthfully which terminals connect to which, and say nothing about the length of a wire or what any of it looks like on the bench.

Where the marks are lost

• Swapping the two energy-storing parts. Each of these questions offers the mirror image of the right answer, so anchor on construction rather than on the phrase: surfaces facing each other across an insulator hold their energy in an electric field, and wire wound into turns holds it in a magnetic one.
• Letting a transformer be the answer to everything. It turns up as a distractor wherever a part must oppose current, be adjusted by hand, or make a signal bigger. A transformer changes the level of an alternating voltage by its turns ratio and takes every watt it delivers from its input, so it cannot supply power gain, which needs an active device.
• Counting circuits when the question counts destinations. The choices are written out as behaviour — how many circuits are worked, and whether each is merely opened and closed or sent to one of two other circuits — so translate the pole-and-throw name into that behaviour before matching, reading the two words separately.
• Accepting a name because it sounds technical. Distractors expand an abbreviation into a device that does not exist, or lend a part the electrode names of a different device family. Check that the name belongs to the family the prompt has just described.
• Treating a diode's drop and bias direction as small print. The forward voltage drop is a normal property whose size depends on the type of diode rather than evidence of a fault, and it does reduce the voltage reaching the load; and a diode does its work — conducting, and in a light-emitting type shining — only while current passes through it in the forward direction, never under the reverse one.
• Handing one alternating-current job to the wrong part. Changing the level of an alternating voltage and turning that alternating current into one that flows in a single direction are two different jobs done by two different parts, and each of them is offered among the other's choices.

Try it yourself