The brightness of a bulb will be reduced,if a resistance is connected in

In the given circuit,find the value of $V$. (in $V$)

$A$ piece of wire of resistance $4\,\Omega$ is bent through $180^o$ at its mid-point and the two halves are twisted together. The new resistance is ............ $\Omega$.

In the given figure,switches $S_{1}$ and $S_{2}$ are initially open. What is the equivalent resistance across $a b$ when the switches $S_{1}$ and $S_{2}$ are closed? (in $\Omega$)

$A$ 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 ................. $W$.

The equivalent resistance across $AB$ would be ............ $\Omega$