Two wires of same metal have the same length but their cross-sections are in the ratio $3:1$. They are joined in series. The resistance of the thicker wire is $10\,\Omega$. The total resistance of the combination will be ............. $\Omega$.

Five identical resistors are initially arranged as shown in the figure by solid lines. If two identical resistors are added as shown by the dashed lines,the change in the equivalent resistance between the initial and final configurations is ....... $\Omega$.

$A$ $3 \ V$ battery with negligible internal resistance is connected as shown in the figure. The current $I$ in the circuit will be ............ $A$.

Two bulbs,one of $200 \ V, 60 \ W$ and the other of $200 \ V, 100 \ W$,are connected in series to a $200 \ V$ supply. The power consumed will be ................ $W$.

$A$ wire of resistance $R$ is bent into a triangular pyramid as shown in the figure,with each segment having the same length. The resistance between points $A$ and $B$ is $R / n$. The value of $n$ is

$A$ heater $A$ gives out $300 \ W$ of heat when connected to a $200 \ V$ $d.c.$ supply. $A$ second heater $B$ gives out $600 \ W$ when connected to a $200 \ V$ $d.c.$ supply. If a series combination of the two heaters is connected to a $200 \ V$ $d.c.$ supply,the heat output will be ................. $W$.