Bulk properties of solids 3 Flashcards
What are the factors on which modules of elasticity of a metal depends?
natured of a material and the manner in which it is deformed.
in stretching a wire work has to be performed why?
when a wire is stretched, the inter atomic forces come into play when these forces oppose the increase in length of the wire. Therefore in order to stretch the wired the work has to be done against the interatomic forces.
Why any metallic part of the machinery is never subjected to a stress beyond the elastic limit of the material?
A permanent deformation will be set up in that metallic part of the machinery.
Name the factors which affect the property of elasticity of a solid.
- presence of impurities,
- change of temperature,
- effect of hammering, rolling and annealing.
Steel is more elastic than rubber explain why?
Consider two wires, one of steel and the other made of rubber. Both the wires are identical that is they possess the same length and the same area cross section. If they are subjected to the same deforming force F, then extension in the steel wire will be less than that in the rubber wire.
Ys=FL/a l’s’
Yr=FL/a l’r’
Ys/Yr = l’r’ / l’s’
since l’s’ < l’r’. it follows that Ys > Yr
A cable is cut into half of its original length. This change has no effect on the maximum load the cable can support?
The breaking stress is a constant for a given material. We know that
breaking load=breaking stress x area of cross section
when the cable is cut to half of its length, the area of cross section does not change., there is no effect on the maximum load (breaking load) , the cable can support
Why do spring balances show wrong readings after they have been used for a long time?
When a spring balance has been used for a long time, the spring in the balanced guest fatigued and there is a loss in elastic strength in the spring. Then, for a given load the extension in the spring is much more and hence the spring balance gives wrong readings.
Why are the bridges declared unsafe after long use?
A bridge undergoes continuous alternating strains a large number of times every day . Therefore, such a long use of the bridge results in the loss of the elastic strength. In other words after a long use, the strain produced is quite large for the given stress and may lead to collapse of the bridge so that it does not happen, the bridges are declared unsafe after a long use.
A heavy virus is suspended from a roof but no weight is attached to the lower end. Is it under stress? justify your answer
A heavy wire (even when no weight is attached to it) It’s under stress, when it is suspended from a roof. Because, the weight of the heavy wire acts as a deforming force.
Why do we prefer steel to copper in manufacturing spring?
a better spring will be the one, in which a large restoring force is developed on being deformed. This, in turn depends upon the elasticity of the material of the spring. As Young’s modulus of spring is greater than the that of copper steel is preferred to manufacture a spring.
Why the stretching of a coil spring is determined by it’s shear modulus
The reason is that when a coil spring is stretched, there is neither a change in the length of the coil (length of the wire forming the coil spring) nor a change in its volume. Since the change takes place in the shape of a coil spring it’s stretching is determined by the sheer modulus.
when a material is under stress, the restoring forces are caused by the inter atomic attraction while under compression of stress, the restoring forces are due to inter atomic repulsion. give reason
When a materials under tensile stress atoms get displaced so that distance between them becomes more than in the normal positions since atoms tries to cone back to the original positions, Restoring force is caused due to the interatomic attraction.
On the other hand, when a compression stress is applied, the atoms get displaced, so that the distance between them becomes less than that in their normal positions. Obviously, when atoms tend to acquire the original positions the restoring force is provided by Inter atomic repulsion.
Why a solid is ductile or brittle?
In the stress vs strain graph for a wire the portion of graph between the elastic limit and breaking point is called plastic region.
A solid is said to be more ductile if the plastic region of the graph is longer and brittle if the plastic region is shorter
