Limit of Proportionality on Spring Graph

Steps:

• Recall Hooke's law: extension is proportional to load, producing a straight line on the graph.
• Identify the linear portion of the extension-load graph, where the spring obeys proportionality.
• Locate the point where the graph deviates from the straight line, marking the end of proportionality.
• Select the option at this deviation point.

Why B is correct:

• B marks the end of the straight-line region, where Hooke's law (F = kx) ceases to hold, defining the limit of proportionality.

Why the others are wrong:

• A: Lies within the linear region, before proportionality limit.
• C: Occurs after deviation, in the non-linear elastic region.
• D: Represents maximum extension, likely yield or plastic deformation point.

Final answer: B