Find the value of current $i_1$ for the circuit shown in the figure. (in $, A$)

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 $\text{ A}$)

What are the uses of a Wheatstone bridge?

In the given electrical circuit,which one of the following equations is correct?

In the circuit shown below,the ammeter reading is zero. Then the value of the resistance $R$ is (in $\Omega$)

The potential at point $E$ for the given figure is ................ $V$.