Two charges QA = +2 μC and QB = - 6μC are located on the x-axis at xA= - 1 cm andxB= +2 cm respectively. Where should a third charge, QC = + 3μC, be placed on the positive x-axis so that the potential at the origin is equal to zero?

Explanation:

Let the third charge Qc = + 3 μC be placed at distance x from origin so that potential at origin due to all charges be zero .

potential due to charge Q at distance d

= k Q / d , k = 9 x 10⁹

so potential due to all charges at origin

9 x 10⁹ x 10⁻⁶   = 0

=

= - 200 + 300

= 100

x = .03 m

3 cm .

+ 3μC should be placed at + 3 cm from origin.