The electric field in the region is $\vec{E} = a\hat{i} + b\hat{j}$ where 'a' and 'b' are constants. The net electric flux passing through a square area of side 'l' parallel to Y-Z plane is

Two point charges $q_1 = 6\ \mu\text{C}$ and $q_2 = 4\ \mu\text{C}$ are kept at points A and B in air where distance $AB = 10$ cm. What is the increase in potential energy of the system when $q_2$ is moved towards $q_1$, by 2 cm ? $\left(\dfrac{1}{4\pi\epsilon_0} = 9 \times 10^9\ \text{SI units}\right)$

For a uniformly charged plane sheet, the variation of electric field (E) with distance (d) is correctly shown graphically in graph

A point charge 'Q' is placed at the centre of the line joining two equal charges '+q' and '+q'. The value of 'Q' when the system is in equilibrium is