If the length of a string is $P$ when the tension in it is $6 \ N$ and its length is $Q$ when the tension in it is $8 \ N$, then the original length of the string is

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

Match List-$I$ with List-$II$ :

List-$I$	List-$II$
$(A)$ $A$ force that restores an elastic body of unit area to its original state	$(I)$ Bulk modulus
$(B)$ Two equal and opposite forces parallel to opposite faces	$(II)$ Young's modulus
$(C)$ Forces perpendicular everywhere to the surface per unit area same everywhere	$(III)$ Stress
$(D)$ Two equal and opposite force perpendicular to opposite faces	$(IV)$ Shear modulus

Choose the correct answer from the options given below:

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 $PQ$.

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

The ratio of radii of two wires of same material is $2: 1$. If these wires are stretched by equal force,the ratio of stresses produced in them is .............