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

Wires $W_{1}$ and $W_{2}$ are made of the same material having a breaking stress of $1.25 \times 10^{9} \, N/m^{2}$. $W_{1}$ and $W_{2}$ have cross-sectional areas of $8 \times 10^{-7} \, m^{2}$ and $4 \times 10^{-7} \, m^{2}$,respectively. Masses of $20 \, kg$ and $10 \, kg$ hang from them as shown in the figure. The maximum mass $m$ that can be placed in the pan without breaking the wires is $..... \, kg$. (Use $g = 10 \, m/s^{2}$)

Anvils made of single crystals of diamond,with the shape as shown in the figure,are used to investigate the behavior of materials under very high pressures. The flat faces at the narrow end of the anvil have a diameter of $0.50 \; mm$,and the wide ends are subjected to a compressional force of $50,000 \; N$. What is the pressure at the tip of the anvil?

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

Why does strain have no unit?

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 $PQ$.