Consider the circuit shown in the figure below:

All the resistors are identical. The ratio $\frac{I}{I^{\text{'}}}$ is

A current of $0.1 \mathrm{A}$ flows through a $25 \mathrm{\Omega }$ resistor represented by the circuit diagram. The current in the $80 \mathrm{\Omega }$ resistor is

Consider the circuit shown below where all resistors are of $1 \mathrm{k\Omega }$. If a current of magnitude $1 \mathrm{mA}$ flows through the resistor marked $X$, what is the potential difference measured between point $P$ and $Q$, 

A light bulb of resistance $R=16 \mathrm{\Omega }$ is attached in series with an infinite resistor network with identical resistances as shown below. A $10 \mathrm{V}$ battery derives a current in the circuit. What should be the value of $r$ such that the bulb dissipates about $1 \mathrm{W}$ of power?

Two rods of copper and iron with the same cross sectional area are joined at $S$ and a steady current $I$ flows through the rods as shown in the figure.

Choose the most appropriate representation of charges accumulated near the junction $S$.