$A$ 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 $n\,?$

Two different metals are joined end to end. One end is kept at a constant temperature and the other end is heated to a very high temperature. The graph depicting the thermo $e.m.f.$ $(E)$ versus temperature $(t)$ is:

$A$ room has an $AC$ running for $5$ hours a day at a voltage of $220$ $V$. The wiring of the room consists of $Cu$ wire of $1$ $mm$ radius and a length of $10$ $m$. Power consumption per day is $10$ commercial units. What fraction of it goes into Joule heating in the wires? What would happen if the wiring is made of aluminium of the same dimensions? $(\rho_{Cu} = 1.7 \times 10^{-8} \, \Omega m, \rho_{Al} = 2.7 \times 10^{-8} \, \Omega m)$

The figure shows a network of four resistances and three batteries. The electrical power dissipated as heat in the circuit is .............. $W$.

Suppose switches $S_1, S_2$ and so on up to $S_6$ are closed one after another in order (first $S_1$,then $S_2$,etc.) at regular intervals of $1 \text{ minute}$ starting from $t = 0$. The graph of current versus time is best represented as:

In the circuit of the adjoining figure,the current through the $12 \ \Omega$ resistor will be ................ $A$.