Orthographic projection concept: If a plane surface is parallel to a given plane of projection, how does it appear in that view?
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ACorrect: it appears in true size and shape as a surface, not as an edge
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BIncorrect: it appears only as an edge (a straight line)
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CDepends on drawing scale only
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DIt always vanishes to a point
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EIt must be hatched instead of shown
Answer
Correct Answer: Correct: it appears in true size and shape as a surface, not as an edge
Explanation
Introduction / Context:This question checks a fundamental rule of orthographic projection used in engineering graphics and technical drawing. Understanding how a geometric plane appears relative to a projection plane (front, top, or side) is essential to produce accurate multiview drawings.
Given Data / Assumptions:
- We are working with principal orthographic views (front, top, side).
- The object contains a flat plane surface (a true geometric plane).
- The plane in question is parallel to one projection plane.
Concept / Approach:In orthographic projection, appearance depends on orientation: (1) If a plane is parallel to a plane of projection, it projects as a surface in true size and true shape. (2) If a plane is perpendicular to a plane of projection, it collapses to a line (an edge) in that view. (3) If a plane is inclined (neither parallel nor perpendicular), it appears foreshortened. The statement in the original stem claimed it would appear “on edge as a straight line,” which is the condition for perpendicularity, not parallelism.
Step-by-Step Solution:
Identify orientation: plane ∥ projection plane.Apply rule: parallel → true size/shape visible in that view.Compare with perpendicular case: perpendicular → line (edge).Conclude: the correct interpretation is that it appears as a surface, not an edge.Verification / Alternative check:Sketch a rectangle lying parallel to the front plane. Its front view shows the full rectangle (true size). Rotate the rectangle 90 degrees so it is perpendicular; the front view collapses to a line. The contrast confirms the rule.
Why Other Options Are Wrong:
- Incorrect: “it appears only as an edge” corresponds to perpendicular orientation, not parallel.
- “Depends on scale” is irrelevant; scale does not change orientation effects.
- “Vanishes to a point” applies to a line perpendicular, not a plane.
- “Must be hatched” is a sectioning convention, unrelated to visibility rules.
Common Pitfalls:Confusing “parallel to view direction” with “parallel to view plane”; mixing up rules for planes vs. edges; assuming foreshortening occurs for parallel planes (it does not).
Final Answer:Correct: it appears in true size and shape as a surface, not as an edge