Fig. shows some of the electric field lines due to three point charges arranged along the vertical axis. All three charges have the same magnitude.
(a) What are the signs of each of the three charges? Explain your reasoning.
(b) At what points(s) is hte magnitude of hte electric field the smallest? Explain your reasoning. Explain how the fields produed by each individual point charge combine to give a small net field at this point or points.
(c ) Two point charges q and -q are placed at a distance d apart. What are the points at which the resultant electric field is parallel to the line joining the two charge?
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Explanation

(a) Top (+), middle (-), bottom(+),
Electric field lines are away form the positve charge and towards the negative charge.

(b) we can get two neutral points in the plane of paper , left and right side of middle charge, i.e. electric field will be zero at these locations.