Load-extension graph identifies spring behavior limits

Steps:

• Load-extension graphs for springs show a straight line initially, where extension is proportional to load per Hooke's law.
• The graph curves after a point, indicating non-proportional behavior.
• Point X marks the end of the straight-line portion.
• This point is defined as the limit of proportionality.

Why B is correct:

• The limit of proportionality is the point where Hooke's law (F = kx) ceases to apply, as the graph deviates from linearity.

Why the others are wrong:

• A: "Limit of force" is not a standard term in spring mechanics.
• C: "Limit of extension" implies maximum stretch, not proportionality.
• D: "Limit of the spring" is vague and does not specify the proportional region.

Final answer: B