A rod of length $L$ having uniform cross-sectional area $A$ is subjected to a tensile force $P$ as shown in the figure below. If the Young’s modulus of the material varies linearly from $E_1$ to $E_2$ along the length of the rod, the normal stress developed at the section-$SS$ is
- $\dfrac{P}{A} \\$
- $\dfrac{P(E_1-E_2)}{A(E_1+E_2)} \\$
- $\dfrac{PE_2}{AE_1} \\$
- $\dfrac{PE_1}{AE_2}$