Find the equivalent resistance between the terminals $X$ and $Y$.

 

The total current supplied to the circuit by the battery is

In the circuit shown, the current through the $4 \mathrm{\Omega }$ resistor is $1 \mathrm{A}$ when the points $P$ and $M$ are connected to a $\mathrm{DC}$ voltage source. The potential difference between the points $M$ and $N$ is

$I-V$ characteristic of a copper wire of length $L$ and area of cross-section $A$ is shown in the figure. The slope of the curve becomes

A voltmeter is connected across 
$\left(\mathrm{i}\right) \mathrm{P}$ and $\mathrm{T}$; $\left(\mathrm{ii}\right) \mathrm{P}$ and $\mathrm{Q}$; $\left(\mathrm{iii}\right) \mathrm{Q}$ and $\mathrm{T}$
Which of these will result in zero reading of voltmeter? Given in circuit - a battery, a resistor, and an open switch.