Hooke's law states that within the elastic limit
- A.Stress is directly proportional to strain
- B.Stress is inversely proportional to strain
- C.Strain is independent of stress
- D.Stress is proportional to the square of the strain
Correct answer
Explanation
The correct answer is A, stress is directly proportional to strain. Hooke found that so long as a body is not strained beyond its elastic limit, the restoring force per unit area rises in step with the fractional deformation, and the constant ratio of the two is called the modulus of elasticity. Option B is wrong because an inverse relation would mean that a stiffer pull produces a smaller deformation, which contradicts every tensile test. Option C is wrong because strain clearly grows with the load applied; if it did not, no wire would ever stretch. Option D is wrong because a square law would make the graph of stress against strain a curve from the very beginning, whereas the first part of a real stress-strain graph is a straight line through the origin. Note that beyond the elastic limit the law fails, and for rubber it does not hold even at small strains.
Read the full article: Elasticity, Stress, Strain and Hooke's Law: Exam Notes
Practice Questions
View allThe SI unit of stress is the
- A.Newton
- B.Joule
- C.Pascal
- D.Watt
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Stress is the restoring force divided by the area over which it acts, so its unit is the newton per square metre, and that combination is given the special name pascal, the same unit used for pressure.
Read the full explanation →Strain is a quantity that has
- A.The unit newton per square metre
- B.No unit and no dimensions
- C.The unit metre
- D.The same unit as energy
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Strain is defined as the change in a dimension divided by the original value of the same dimension, a length divided by a length or a volume divided by a volume, so the units cancel and only a pure number survives.
Read the full explanation →The ratio of longitudinal stress to longitudinal strain within the elastic limit is called
- A.Bulk modulus
- B.Modulus of rigidity
- C.Young's modulus
- D.Poisson's ratio
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It governs the stretching or compression of a wire or rod along its length and is obtained by dividing the force per unit area of cross section by the fractional change in length.
Read the full explanation →The reciprocal of the bulk modulus of a material is known as its
- A.Compressibility
- B.Rigidity
- C.Ductility
- D.Tenacity
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The bulk modulus measures how strongly a substance resists a change in volume under uniform pressure, so its reciprocal measures how readily the volume yields, and that quantity is called compressibility.
Read the full explanation →Which of the following statements about steel and rubber is correct in physics?
- A.Rubber is more elastic because it stretches more
- B.Steel is more elastic because its modulus of elasticity is much larger
- C.Both have equal elasticity
- D.Neither is elastic, since both are solids
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Elasticity in physics is not the ability to stretch far but the strength of the restoring tendency, measured by the stress needed to produce a given strain, and steel demands an enormously greater stress than rubber for the same fractional extension.
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