charges q and –3q are placed fixed on x-axis separated by distance ‘d’. Where should a third charge 2q be placed such that it will not experience any force?

Distance between -3q and q is =d


Let us consider


Distance between q and 2q is = x


Then 2q must be placed at a distance =(d+x)


Now we have to find out the x


From Coulomb’s law


The force exerted by one charge on another charge is



From -3q to 2q is



From q to 2q is



Compare (1) and (2)






(Or)



1