Schematic literacy — variable inductor symbols: In standard electronics notation, not every inductor symbol shown in reference figures indicates a variable inductor. Assess the claim that “all the illustrated inductor symbols are variable inductors.”

Introduction / Context:
Reading schematics accurately requires recognizing graphical cues. Inductors can be fixed or variable. Variable types are shown with clear modifiers (for example, an arrow through the coil or an adjustable core indicator). This question addresses whether all commonly shown coil symbols necessarily indicate variability.

Given Data / Assumptions:

• Standard IEC/ANSI symbol conventions.
• Variable components are marked with adjustment indicators (arrow, diagonal slash, or movable core symbol).
• Plain coil symbols without modifiers denote fixed inductors.

Concept / Approach:
Symbol semantics: a base coil symbol indicates an inductor. Added annotation conveys special properties: iron core (lines/slug), tapped coil (tap symbol), or adjustability (arrow). Therefore, unless an adjust feature is explicitly drawn, one must assume the inductor is fixed. Stating that “all shown symbols are variable” is overgeneralization and incorrect.

Step-by-Step Solution:

Verification / Alternative check:
Cross-reference with any electronics symbol chart: you will find separate entries for “inductor,” “variable inductor,” “tapped inductor,” and “iron-core inductor,” confirming the need for explicit modifiers to signal adjustability.

Why Other Options Are Wrong:

• Every inductor symbol implies adjustability: Incorrect; adjustability must be shown.
• Valid only in RF schematics / depends on core / many turns: RF usage, core material, or drawing style does not change the meaning of the symbol modifiers.

Common Pitfalls:
Assuming an iron-core or slugged symbol is always adjustable; confusing tapped inductors with variable inductors; misreading an arrow that actually denotes a variable resistor nearby.

Final Answer:
Incorrect — only symbols with an adjust arrow/slug are variable