Five resistors are connected as shown in the diagram. The equivalent resistance between $A$ and $B$ is .............. $\Omega$.

Calculate the equivalent resistance between $A$ and $B$.

If ${V_{AB}} = 4\,V$ in the given figure,then resistance $X$ will be .............. $\Omega$.

Find the current flowing through the resistance $R_1$ of the circuit shown in the figure,if the resistances are equal to $R_1=10 \Omega, R_2=20 \Omega$,and $R_3=30 \Omega$,and the potentials of points $1, 2$,and $3$ are equal to $\phi_1=10 \text{ V}, \phi_2=6 \text{ V}$,and $\phi_3=5 \text{ V}$. (in $\text{ A}$)

Why is the circuit configuration known as a Wheatstone bridge?

The current in the arm $CD$ of the circuit will be