Apoint charge of 4 μс is located at x =-30 cm, and a second point charge of-10 pc is located at x-+4.0 cm. where should a third charge of +6.0 pc be placed so that the electric field at x = 0 is zero?

it is to be placed at x = 3.1 cm

Explanation:

Electric field due to charge placed at x = -30 cm

so we have

towards left

now electric field due to another charge placed at x = 4 cm

towards Right

now we need electric field due to 6 pC must be equal to

towards Left

so we have

so it is to be placed at x = 3.1 cm

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