(a) (i) Two point charges $+q$ and $-q$ are held at $(a, 0)$ and $(-a, 0)$ in x-y plane. Obtain an expression for the net electric field due to the charges at a point $(0, y)$. Hence, find electric field at a far off point ($y \gg a$). (ii) Three point charges of $-2\text{ nC}$, $-1\text{ nC}$, and $+5\text{ nC}$ are kept at the vertices $ ext{A}$, $ ext{B}$ and $ ext{C}$ of an equilateral triangle of side $0\cdot2\text{ m}$. Find the total amount of work done in shifting the charges from $ ext{A}$ to $ ext{A}_1$, $ ext{B}$ to $ ext{B}_1$ and $ ext{C}$ to $ ext{C}_1$. Here $ ext{A}_1$, $ ext{B}_1$ and $ ext{C}_1$ are the midpoints of sides $ ext{AB}$, $ ext{BC}$ and $ ext{CA}$, respectively.