$A$ charge $10^{-9} \ C$ is located at the origin of a coordinate system and another charge $Q$ at $(2, 0, 0) \ m$. If the $Y$-component of the electric field at $(3, 1, 1) \ m$ is zero,calculate the value of $Q$.

Four charges $+q, +2q, +q$ and $-2q$ are placed at the corners $A, B, C$ and $D$ of a square respectively. The force on a unit positive charge kept at the centre $O$ is

Point charges $+8q$ and $-2q$ are placed at $x = 0$ and $x = L$ respectively. At which point on the $X$-axis will the resultant electric field intensity be zero?

The electric field at the centre $O$ of a semicircle of radius $a$ having a linear charge density $\lambda$ is given by:

Six point charges are placed at the vertices of a regular hexagon of side $a$ as shown in the figure. Three charges are $+Q$ and three are $-Q$ arranged alternately. The electric field intensity at a point on the line passing through the centre $O$ and perpendicular to the plane of the figure at a large distance $x (x \gg a)$ from $O$ is (Let $\frac{1}{4 \pi \epsilon_0} = k$):

$A$ cube of a metal is given a positive charge $Q$. For the above system,which of the following statements is true?