The equivalent resistance between points $A$ and $B$ in the following circuit is:

Figure $(i)$ below shows a Wheatstone's bridge in which $P, Q, R$ and $S$ are fixed resistances,$G$ is a galvanometer and $B$ is a battery. For this particular case,the galvanometer shows zero deflection. Now,only the positions of $B$ and $G$ are interchanged,as shown in figure $(ii)$. The new deflection of the galvanometer

$ABCD$ is a square where each side is a uniform wire of resistance $1\,\Omega$. $A$ point $E$ lies on $CD$ such that if a uniform wire of resistance $1\,\Omega$ is connected across $AE$ and a constant potential difference is applied across $A$ and $C$,then $B$ and $E$ are equipotential.

Find the current through the branch $ad$ of the circuit shown in the figure. (in $, A$)

The value of current through the $20\,\Omega$ resistor is ............ $A$.

In the given circuit,calculate the potential difference between points $P$ and $Q$ in $volt$.