When a spiral spring is stretched by suspending a load on it,the strain produced is called

When a force $F_1$ is applied on a metallic wire,the length of the wire is $L_1$. If a force $F_2$ is applied on the same wire,the length of the wire is $L_2$. The original length of the wire $L$ is

Below are two statements. One is labeled as Assertion $(A)$ and the other as Reason $(R).$
Assertion $(A):$ The property of an object that allows it to regain its original shape after the external force applied to it is removed is called elasticity.
Reason $(R):$ The restoring force depends on the intermolecular and interatomic forces in a solid.
In the context of the above statements,choose the most appropriate answer from the options given below:

The load versus elongation graph for four wires of the same material is shown in the figure. The thinnest wire is represented by the line

Consider a long steel bar under a tensile stress due to force $F$ acting at the edges along the length of the bar (as shown in figure). Consider a plane making an angle $\theta$ with the length. What are the tensile and shearing stresses on this plane?
$(a)$ For what angle is the tensile stress a maximum?
$(b)$ For what angle is the shearing stress a maximum?

What should be the shape of the pillars or columns in buildings and bridges?