JEE Main 2019 Physics question
Four point charges −q, +q, +q and −q are placed on y-axis at y = −2d, y = −d, y = +d, y = +2d, respectively. The magnitude of the electric field E at a point on the x-axis at x = D, with D >> d, will behave as:
Answer: (C)
Solution
Net charge and dipole moment are zero; the arrangement is a quadrupole, whose field falls as .