In the figure,the area of each plate is $A$ and the distance between consecutive plates is $d$. What is the effective capacitance between points $A$ and $B$?

For the given circuit,find the charge on the $4\ \mu F$ capacitor in $\mu C$.

In the circuit shown,the cell is ideal,with $emf$ $=$ $15$ $V$. Each resistance is of $3$ $\Omega$. The potential difference across the capacitor is.....$V$.

Assertion: Charges are given to plates of two plane parallel plate capacitors $C_1$ and $C_2$ (such that $C_2 = 2C_1$) as shown in the figure. Then the key $K$ is pressed to complete the circuit. Finally,the net charge on the upper plate and the net charge on the lower plate of capacitor $C_1$ is positive.
Reason: In a parallel plate capacitor,both plates always carry equal and opposite charge.

The dielectric strength of air is $E = 3 \times 10^6 \ V/m$. What is the maximum charge that can be given to a sphere of diameter $6 \ m$? (in Coulombs)

Three point charges $1 \ C$,$-2 \ C$,and $-2 \ C$ are placed at the vertices of an equilateral triangle of side $1 \ m$. The work done by an external force to increase the separation of the charges to $2 \ m$ in joules is ($\varepsilon_0 =$ permittivity of air).