If a battery of voltage $V$ is connected across terminals $I$ of the black box shown in the figure,an ideal voltmeter connected to terminals $II$ gives a reading of $V/2$. While if the battery is connected to terminals $II$,a voltmeter across terminals $I$ reads $V$. The black box may contain:

$A$ thermocouple produces $200\,\mu V$ between $0\,^oC$ and $100\,^oC$. If it produces $64\,\mu V$ and $76\,\mu V$ for temperature ranges $(0\,^oC - 32\,^oC)$ and $(32\,^oC - 70\,^oC)$ respectively,then the thermo $emf$ produced between $70\,^oC$ and $100\,^oC$ will be ........... $\mu V$.

Which of the following graphs represents the variation of power loss in the external load with external resistance $R$?

$A$ copper voltameter is connected in parallel with a heater coil of resistance $0.1\,\Omega$. $A$ current is passed for $20\,\text{minutes}$,resulting in the deposition of $0.99\,\text{g}$ of copper on the cathode. If the electrochemical equivalent of copper is $0.00033\,\text{g/C}$,the heat produced in the coil is ........... $J$.

Answer the following questions:
$(a)$ $A$ steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor: current, current density, electric field, drift speed?
$(b)$ Is Ohm's law universally applicable for all conducting elements? If not, give examples of elements which do not obey Ohm's law.
$(c)$ $A$ low voltage supply from which one needs high currents must have very low internal resistance. Why?
$(d)$ $A$ high tension $(HT)$ supply of, say, $6 \ kV$ must have a very large internal resistance. Why?

$A$ battery of $emf$ $E$ is being charged from a charger such that the positive terminal of the battery is connected to terminal $A$ of the charger and the negative terminal of the battery is connected to terminal $B$ of the charger. The internal resistance of the battery is $r$.