In a crystal,the atoms are located at the position of

Two equal and opposite forces are exerted on a bar (rod) as shown in the figure. The plane $PQ$ makes an angle $\theta$ with the cross-section $PR$ (having area $a$). Find the tensile stress on the plane $PQ$.

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

What is the slope of the graph of stress $\to$ strain up to the elastic limit?

If the length of a wire is doubled,what is the strain?

What is strain? Give its units. Define longitudinal stress.