12. A charge of + 10 C is located at the point x = 0 and y = 1 and charge of - 5C is at the point
x = 0 and y = - 1. Find the point on y axis at which net $E$ = 0.
[Ans.: (0, -5.828, 0) or (0, -0.1716, 0)]
13. A point charge of 20 nC is located at the origin. Determine the magnitude and direction of $E$ at
point P (1, 3, -4) m.
[Ans. : 1.357 $\vec{a_x}$ + 4.073 $\vec{a_y}$ - 0.784 $\vec{a_z}$ V/m]