In the circuit shown in the figure,find the current through the $4\,\Omega$ resistor.

$A$ cell of emf $E$ is connected to a resistance $R_{1}$ for time $t$ and the amount of heat generated in it is $H$. If the resistance $R_{1}$ is replaced by another resistance $R_{2}$ and is connected to the cell for the same time $t$, the amount of heat generated in $R_{2}$ is $4H$. Then the internal resistance $r$ of the cell is:

Consider the following two statements $A$ and $B$,and identify the correct choice out of the given answers:
$A$. Thermo $e.m.f.$ is minimum at the neutral temperature of a thermocouple.
$B$. When two junctions made of two different metallic wires are maintained at different temperatures,an electric current is generated in the circuit.

$A$ steel wire has a resistance twice that of an aluminium wire. Both of them are connected to a constant voltage supply. More heat will be dissipated in:

The current flowing through a copper voltameter is $1.5\ A$. If the surface area of the electrode plate is $50\ cm^2$,the thickness of the copper layer deposited on this surface in $20\ min$ will be: (Density of copper = $9000\ kg/m^3$ and Electrochemical equivalent of copper = $0.00033\ g/C$)

In the given circuit,with steady current,the potential drop across the capacitor must be