The Hooke's law is valid for
- A.only proportional region of the stress-strain curve
- B.entire stress-strain curve
- C.entire elastic region of the stress-strain curve
- D.elastic as well as plastic region of the stress-strain curve
Correct answer
Explanation
The correct answer is A, only proportional region of the stress-strain curve. Hooke's law says stress is directly proportional to strain, and that holds only up to the proportional limit, where the curve is a straight line.
On a stress-strain graph of a metal wire, the first part is a straight line from the origin; its slope is the modulus of elasticity (Young's modulus). Beyond the proportional limit the curve bends, yet the wire still returns to its original length up to the elastic limit. After the yield point the material deforms plastically and keeps a permanent set, and finally it breaks at the fracture point.
Option B is wrong because the law fails well before the breaking point. Option C is wrong because a small part of the elastic region, between the proportional limit and the elastic limit, is not linear. Option D is wrong because in the plastic region strain grows without a proportional rise in stress.
Exam tip: order on the curve = proportional limit, elastic limit, yield point, ultimate stress, fracture; Hooke's law only up to the first.
Practice Questions
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- D.Urea is produced in lung and kidney.
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- D.Eyepiece-Objective lens-Body tube-Mirror
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- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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- A.A particular pattern of equidistant stars from the earth in the sky
- B.A particular pattern of stars that may not be equidistant from the earth in the sky
- C.A particular pattern of planets of our solar system in the sky
- D.A particular pattern of stars, planets and satellites in the sky due to their position in the space
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