Copper of fixed volume $V$ is drawn into a wire of length $l$. When this wire is subjected to a constant force $F$,the extension produced in the wire is $\Delta l$. Which of the following graphs is a straight line?

$A$ rigid bar of mass $15 \, kg$ is supported symmetrically by three wires,each $2 \, m$ long. The wires at each end are made of copper,and the middle one is made of steel. The Young's modulus of elasticity for copper and steel are $110 \times 10^9 \, N/m^2$ and $190 \times 10^9 \, N/m^2$ respectively. If each wire is to have the same tension,the ratio of their diameters (diameter of copper wire to diameter of steel wire) will be ............

The length of an iron wire is $L$ and the area of cross-section is $A$. The increase in length is $l$ upon applying a force $F$ on its two ends. Which of the following statements is correct?

$A$ metal rod of Young's modulus $Y$ and coefficient of linear expansion $\alpha$ has its temperature raised by $\Delta \theta$. The linear stress required to prevent the expansion of the rod is:

The following four wires are made of the same material. If the same tension is applied to each,the wire having the largest extension is

The pressure to be applied to the ends of a steel cylinder to keep its length constant upon raising its temperature by $100^{\circ} C$ is (thermal expansion coefficient, $\alpha = 11 \times 10^{-6} / K$, Young's modulus $Y = 200 \text{ GPa}$)