A point charge of +3.0 mC is located at the origin of a coordinate system and a second point charge of -6.0 mC is at x = 1.0 m.At what point on the x axis is the electrical potential zero?
A)-0.25 m
B)+0.25 m
C)+0.33 m
D)+0.75 m

Question

Quizplus · Accepted Answer

The electric potential due to a point charge is given by V=kq/r, where k is the Coulomb constant (9x10^9 Nm^2/C^2), q is the charge of the particle and r is the distance between the particle and the point at which potential is to be calculated. 
For potential to be zero, the two charges must cancel each other out. Let the point on the x-axis at which potential is to be calculated be x. Then, 
V_1 = kq_1/r_1 = k(3x10^-3)/x
V_2 = kq_2/r_2 = k(-6x10^-3)/(1-x) 
For potential to be zero, V_1 + V_2 = 0. 
Substituting the above values and solving, we get x=0.33 m.

Therefore, the answer is C.

A Point Charge of +3