Two very long line charges of uniform charge densities +λ and -λ are placed along same line with the separation between the nearest ends being 2a , as shown in figure. The electric field intensity at point O is

The field at O due to small element dx isdE=14πε0λdxx2 Hence, due to one wire, E1=∫a∞ 14πε0⋅λdxx2E1=14πε0⋅λa towards left Similarly, Electric field at O due to other wire,E2=14πε0⋅λa toward left ∴ Net field at O is E=2×14πε0λa=λ2πε0a