Two charges 9e and 3e are placed at a certain distance r.The distance of the point where the electric field intensity will be zero is:

Dear student,
Let distance at which electric field intesity is zero be 'a' from 9e charge.
so putting formula, the electric field for 3e and 9e will be equal,
1/(4*pi*epsilon0) *(9e/a^2)=1/(4*pi*epsilon0)* (3e/(r-a)^2)
=>3(r-a)^2 = a^2
solving we get,
a= r*sqrt(3)/(sqrt(3)+1)= r*(3-sqrt(3))/2 [Ans]
Regards,
Thank you,
Soumya Ranjan Mohanty.