What is the equivalent resistance between $A$ and $B$ in the given circuit (in $\Omega$)?

What is a Wheatstone bridge? Explain its principle.

In a typical Wheatstone network,the resistances in cyclic order are $A = 10 \,\Omega $,$B = 5 \,\Omega $,$C = 4 \,\Omega $ and $D = 4 \,\Omega $. What should be done for the bridge to be balanced?

Consider the circuit shown in the figure where all the resistances are of magnitude $1 k \Omega$. If the current in the extreme right resistance $X$ is $1 mA$, the potential difference between $A$ and $B$ is: (in $V$)

In a Wheatstone bridge (see figure),resistances $P$ and $Q$ are approximately equal. When $R = 400 \,\Omega$,the bridge is balanced. On interchanging $P$ and $Q$,the value of $R$ for balance is $405 \,\Omega$. The value of $X$ is close to ................. $\Omega$. (in $.5$)

$ABCD$ 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.