Question

point charges +1 micro coulomb and +4 microcoulomb are separated by a distance 4cm in air what is the distance of a null point from the small charge? what is the electric potential at null point?

Answer 1

the electric oppose, and where they are equal and opposite... x is the distance from the smaller charge
k/(x^2)=k4/(x-.04)^2

4x^2=x^2-.08x+.04^2

3x^2+.08x-.0016=0

x=(-.08+-sqrt(.0064+12*.0015))/6

x= 0.0127m=1.27cm from smaller charge

potential=k(1/1.27+4/(4-1.27))