Silver and copper voltameters are connected in parallel with a battery of $e.m.f.$ $12\, V$. In $30$ minutes,$1\, g$ of silver and $1.8\, g$ of copper are liberated. The power supplied by the battery is ...................... $J/s$ ($Z_{Cu} = 6.6 \times 10^{-4}\,g/C$ and $Z_{Ag} = 11.2 \times 10^{-4}\,g/C$).

$A$ $3\,^oC$ rise in temperature is observed in a conductor by passing a certain current. When the current is doubled,the rise in temperature will be ............. $^oC$.

When a current is passed through water,acidified with a dilute sulphuric acid,the gases formed at the platinum electrodes are

In the circuit as shown in the figure, the:

$A$ battery consists of a variable number $n$ of identical cells (each having electromotive force $\varepsilon$ and internal resistance $r$) which are connected in series. The terminals of the battery are short-circuited and the current $I$ is measured. Which of the graphs shows the correct relationship between $I$ and $n\,?$

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?