Two point charges 4 micro coulomb & -2 micro coulomb are seperated by a distance of 1m in air. At what point of line joining the charges is the electric potential zero?

This point can be found out by taking the algebraic sum of the potential due to both the charges equal to zero.

For example if we place two positive charges Q and q are placed at a distance r apart then find the point at which potential is zero.

We find it by considering a point at a distance x from charge Q on the joining line. Thus,

here

r = 1m

Q = 4 μC

q = -2 μC

so,

V_Q + V_q = 0

or

kQ / x + kq / (r-x) = 0

or

4μC / x  -  2μC / (1-x) = 0

or

4/x = 2/(1-x)

or

6x = 4

thus, the point at which potential would be zero will be at

x = 2/3 = 0.66 m