Which one of the following does not generally obey Hooke's law?
- A.Glass
- B.Quartz
- C.Clay
- D.Copper
Correct answer
Explanation
The correct answer is C, Clay. Clay is a plastic material: it deforms permanently under even a small force, so its stress is not proportional to its strain.
Hooke's law says that within the elastic limit, stress is directly proportional to strain, and the constant of proportionality is the modulus of elasticity. A body that obeys it returns to its original shape when the force is removed. Metals such as copper and steel follow the law over a range of small strains. Quartz is almost a perfectly elastic body, which is why quartz fibres are used in sensitive torsion balances. Glass is brittle but elastic until it breaks. Putty, wet clay and dough have practically no elastic range and keep whatever shape they are pressed into.
A is wrong because glass obeys Hooke's law up to its breaking point. B is wrong because quartz is the classic near-perfect elastic material. D is wrong because copper obeys the law for small strains before it yields.
Exam tip: quartz ≈ perfectly elastic; clay, putty ≈ perfectly plastic.
Practice Questions
View allWhich one of the following is not used as fertilizer?
- A.Ammonium nitrate
- B.Ammonium sulphide
- C.Ammonium phosphate
- D.Ammonium sulphate
Show answer
Ammonium sulphide is an unstable, foul-smelling compound that breaks down to release ammonia and toxic hydrogen sulphide, so it is not used as a fertiliser.
Read the full explanation →The focal length of the objective lens of a telescope is 50 cm. If the magnification of the telescope is 25, then the focal length of the eye-piece is
- A.12.5 cm
- B.5 cm
- C.2 cm
- D.10 cm
Show answer
For an astronomical telescope in normal adjustment the magnifying power equals the focal length of the objective divided by that of the eyepiece, so the eyepiece focal length is 50 ÷ 25 = 2 cm.
Read the full explanation →The major source of vitamins and minerals for vegetarians is
- A.black gram and wheat.
- B.rice and mustard.
- C.vegetables and fruits.
- D.soya bean and milk.
Show answer
Vegetables and fruits supply most of the vitamins and minerals in a vegetarian diet, which is why they are called protective foods.
Read the full explanation →Which one of the following compounds is used in black and white photography?
- A.AgF
- B.AgBr
- C.AgCl
- D.Ag2SO4
Show answer
Silver bromide is the light-sensitive compound coated on black and white photographic film and paper, because light breaks it down into tiny grains of silver metal.
Read the full explanation →Which one of the following statements about speed and velocity is correct?
- A.Speed and velocity both are vector quantities.
- B.Speed and velocity both are scalar quantities.
- C.Speed is vector quantity and velocity is scalar quantity.
- D.Speed is scalar quantity and velocity is vector quantity.
Show answer
Speed tells only how fast a body moves, while velocity also tells the direction of motion, and a quantity with both magnitude and direction is a vector.
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