Four point charges - q,+ q,+ q and -q are placed on y -axis at y=-2 d, y=- d, y=+ d and y=+2 d, respectively. The magnitude of the electric field E…

Four point charges $\displaystyle -\mathrm{q},+\mathrm{q},+\mathrm{q}$ and -q are placed on $\displaystyle y$-axis at $\displaystyle y=-2 \mathrm{~d}, y=-\mathrm{d}$, $\displaystyle y=+\mathrm{d}$ and $\displaystyle y=+2 \mathrm{~d}$, respectively. The magnitude of the electric field E at a point on the $\displaystyle x$-axis at $\displaystyle x=\mathrm{D}$, with $\displaystyle \mathrm{D} \gg \mathrm{d}$, will behave as: