In the circuit of the adjoining figure, the current through $12 \mathrm{\Omega }$ resistor will be

  

The circuit is shown in the following figure. The potential at points $A, B, C, D$ and $O$ are given. The currents in the resistances $R_1, R_2$ and $R_3$ are in the ratio of $4:2:1$ What is the ratio of resistances $R_1, R_2, R_3$ and $R_4$?

In the circuit as shown in figure, if the current drawn through battery is $0.5 \mathrm{A}$. Then

Consider a simple circuit shown in figure stands for a variable resistance $R^{\text{'}}$. $R^{\text{'}}$ can vary from $R_0$ to infinity, $r$ is internal resistance of the battery $\left(r<<R<<R^{\text{'}}\right)$.