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CAIE IGCSE Physics Limit of Proportionality

Practise defining and locating the limit of proportionality on load-extension graphs and distinguishing the straight Hooke's-law region from the curved response beyond it.

Syllabus
2026–2028
Course
Physics 0625

Exam points

  • define the limit as the greatest load for which extension remains directly proportional to load
  • identify the end of the straight constant-gradient region on a load-extension graph
  • sketch a straight line through the origin up to the limit, then a curve with changing gradient

1.5.1.10—Term ‘limit of proportionality’ for a question 1

[Maximum number: 2]

A force is a vector quantity.

A student suspends a spring from a clamp stand and measures the length l0l_{0} of the spring.

Fig. 2.1 shows the apparatus.

Fig. 2.1 (not to scale)

Fig. 2.1 (not to scale)

The student then suspends loads of different weights from the spring and measures the length of the spring for each load. He then plots a graph of the length of the spring against weight.

Fig. 2.2 is the graph that the student plots.

Fig. 2.2

Fig. 2.2

State what is meant by the limit of proportionality and, using Fig. 2.2, determine the weight of the load that causes this spring just to reach the limit of proportionality.
limit of proportionality
weight =

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