The breaking stress of a wire depends upon
- A.The length of the wire
- B.The radius of the wire
- C.The material of the wire
- D.The shape of the cross-section
Correct answer
Explanation
The correct answer is C, the material of the wire. Breaking stress is the greatest force per unit area that a substance can bear before it snaps, and since both the force and the area are already accounted for in the definition, what remains is a constant of the substance itself, the same for a thin wire and a thick cable of the same metal. Option A is wrong because length does not enter; a long wire and a short wire of the same steel break at the same stress, although the breaking load in newton is also the same, not the stress. Option B is wrong because a thicker wire holds a larger load exactly in proportion to its larger area, leaving the stress unchanged. Option D is wrong for the same reason, since only the amount of area matters and not its outline. The quantity that does depend on length and area is the extension produced by a given load.
Read the full article: Elasticity, Stress, Strain and Hooke's Law: Exam Notes
Practice Questions
View allHooke'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
Show answer
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.
Read the full explanation →The SI unit of stress is the
- A.Newton
- B.Joule
- C.Pascal
- D.Watt
Show answer
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
Show answer
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
Show answer
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
Show answer
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 →