Doubly ionised helium atom and hydrogen ions are accelerated, from rest, through the same potential difference. The ratio of final velocities of helium and hydrogen is

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

In the shown circuit, what is the potential difference across $A$ and $B$ ?

The graphs between current $\left(I\right)$ and voltage $\left(V\right)$ for three linear resistors $1$, $2$ and $3$ given below.

If $R_1, R_2$ and $R_3$ are the resistances of these resistors, then which one of the following is correct?

What is the current in the $4 \mathrm{\Omega }$ resistor when switch $S_1$ is open and switch $S_2$ is closed in the given circuit?