A technician tests two different springs, Spring A and Spring B, by applying the same increasing force to each one. Spring A has a higher spring constant than Spring B. Describe what is meant by the term 'spring constant' and explain how the behaviour of Spring A will differ from that of Spring B when the same force is applied to each spring.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Spring A has a spring constant of 80 N/m. Spring B has a spring constant of 20 N/m.
Model answer (4 marks)
The spring constant (k) is a measure of a spring’s stiffness – it is the force required to produce one metre of extension, so k = F/Δx. A higher k means a stiffer spring.
Because Spring A has a higher k than Spring B, for the same applied force it will extend less. Both springs obey Hooke’s Law (F = kΔx) while the force is below the elastic limit, so the extension is directly proportional to the force. If the force exceeds the elastic limit, the spring will deform plastically and will not return to its original length when the force is removed.
Because Spring A has a higher k than Spring B, for the same applied force it will extend less. Both springs obey Hooke’s Law (F = kΔx) while the force is below the elastic limit, so the extension is directly proportional to the force. If the force exceeds the elastic limit, the spring will deform plastically and will not return to its original length when the force is removed.
Examiner tips
- Define k as force per metre of extension; mention stiffness.
- State that higher k = less extension for same force.
- Show Hooke’s Law applies below elastic limit.
- Note plastic deformation beyond elastic limit.
Common mistakes
- Confusing spring constant with spring mass or length.
- Saying the spring with higher k extends more instead of less.
- Ignoring the elastic limit and plastic deformation.
Mark scheme (4 marks)
- The spring constant is a measure of a spring's stiffness / the force required to extend a spring per metre of extension.
- Spring A (higher spring constant) will extend less than Spring B for the same applied force.
- Both springs obey Hooke's Law while the force is below the limit of proportionality, meaning extension is directly proportional to the applied force.
- Beyond the elastic limit, the spring will undergo plastic distortion and will not return to its original shape when the force is removed.
Key terms in this question
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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