🔧 Components, Symbols and AC vs DC

Part 1 of 7 — Components on the ASVAB

Topic Overview

What These Questions Look Like

Electronics Information has 15 questions in 10 minutes on the CAT-ASVAB (about 40 seconds each). Many of them are quick identification questions:

• "What does this component do?" (A diode lets current flow in only one direction.)
• "Which symbol is a ...?" (a small schematic drawing with four choices)
• "What is the unit of ...?" (capacitance is measured in farads)
• "What is AC?" (alternating current: it reverses direction many times a second)

These are recall questions: you either know the part or you don't, so they are fast points once you learn the list below.

The Component Cheat Sheet

🔧 Components, Symbols and AC vs DC

Part 2 of 7 — Schematic Symbols, Switches and Circuit Protection

Why Symbols

A schematic is a wiring map drawn with standard symbols instead of pictures. Anyone trained in electronics can read one, and the ASVAB expects you to recognize the common symbols at a glance.

The gallery on the next screen shows the symbols for this part. Study the shape of each one: on the test, the label will not be there.

🔧 Components, Symbols and AC vs DC

Part 3 of 7 — Resistors, Capacitors and Inductors

Resistors

A resistor limits current and drops voltage. Most are fixed (one value). Some are variable:

The resistor color code

Small resistors are marked with colored bands instead of printed numbers. For a four-band resistor, start from the end where the bands are bunched together:

• Band 1: first digit
• Band 2: second digit
• Band 3: multiplier (how many zeros to add)
• Band 4: tolerance: gold = ±5%, silver = ±10%

A memory sentence for the order Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White: "Better Be Right Or Your Great Big Venture Goes West."

Worked example (Figure 4). Yellow (4), violet (7), red (2 zeros), gold: 47 followed by two zeros = 4,700 Ω (4.7 kΩ), ±5%.

Another. Brown (1), black (0), orange (3 zeros): 10,000 Ω = 10 kΩ.

🔧 Components, Symbols and AC vs DC

Part 4 of 7 — Diodes, Transistors and Transformers

Semiconductors in One Paragraph

Diodes and transistors are made of semiconductors, usually silicon (sometimes germanium). Adding tiny amounts of other elements (doping) makes N-type material (extra free electrons, negative carriers) or P-type material (missing electrons, called holes, which act as positive carriers). Where P and N meet, a junction forms that lets current cross easily in one direction only.

Diodes: One-Way Valves

A diode is one P-N junction. It conducts when its anode is more positive than its cathode (forward bias) and blocks current when connected the other way (reverse bias).

• In the symbol, the triangle points the way conventional current flows, and the bar is the cathode. (On a real diode, a painted stripe marks the cathode end.)
• A rectifier uses diodes to change AC into DC. One diode lets through only half of each AC cycle (half-wave); four diodes in a bridge use both halves (full-wave).
• An LED (light-emitting diode) gives off light when current flows forward.
• A zener diode is designed to conduct backwards at a set voltage, so it is used to regulate (hold steady) a voltage.

History note: Before semiconductors, the same jobs were done by vacuum tubes (electron tubes): a tube diode rectified, a tube triode amplified. Tubes are larger, run hot and burn out; diodes and transistors replaced them in almost everything.

🔧 Components, Symbols and AC vs DC

Part 5 of 7 — AC vs DC, Frequency and Household Wiring

Two Kinds of Current

AC won the battle to power homes because transformers can step it up to very high voltage for long-distance transmission (high voltage means low current, so less energy is lost as heat in the lines) and back down to safe levels near your house.

Many devices run on DC inside but plug into AC: their power supply uses a transformer to lower the voltage and a rectifier to turn it into DC.

🔧 Components, Symbols and AC vs DC

Part 6 of 7 — Component Test Strategy and Common Traps

Timing

CAT-ASVAB EI: 15 questions, 10 minutes, about 40 seconds each (paper: 20 questions in 9 minutes). Component and symbol questions are pure recall, so aim for 10 to 15 seconds each and save the extra time for circuit calculations.

Remember the CAT rules: you can't return to a question, you must answer to move on, and any question could be an unscored tryout, so treat each as scored. If time is short, keep answering genuinely; a burst of random answers at the end is penalized heavily.

A recall routine

1. Name what the part does before you look at the choices (diode → one way).
2. Check the unit if the question asks for one (capacitor → farads).
3. Picture the symbol if one is shown: shape first, then details (triangle + bar = diode; which way is the triangle pointing?).
4. Eliminate by job: a choice that describes another part's job is wrong even if it sounds technical.

Pairs the test likes to swap

🔧 Components, Symbols and AC vs DC

Part 7 of 7 — Mixed Mastery Set

Ten questions covering the whole topic at real EI difficulty. Aim for about 40 seconds each, and much less on the recall items.