Limit of Proportionality on Load-Extension Graph

Steps:

• Recall Hooke's law: extension is directly proportional to load up to the limit of proportionality, producing a straight line on the graph.
• Examine the graph for the straight-line portion ending where curvature begins.
• The limit of proportionality is the last point on this straight line before deviation.
• Select the option at that transition point.

Why A is correct:

• A marks the end of the linear region, where load is proportional to extension per Hooke's law (F = kx).

Why the others are wrong:

• B is beyond the straight line, in the non-proportional region.
• C is further along the curve, possibly in plastic deformation.
• D is at maximum load or breaking point, not proportionality limit.

Final answer: A