Which device can convert all electrical energy into heat

$A$ wire of length $L$ and $3$ identical cells of negligible internal resistances are connected in series. Due to the current, the temperature of the wire is raised by $\Delta T$ in time $t. N$ number of similar cells is now connected in series with a wire of the same material and cross section but of length $2L$. The temperature of the wire is raised by the same amount $\Delta T$ in the same time $t$. The value of $N$ is :

Two resistors of $6\,\Omega $ and $9\,\Omega $ are connected in series to a $120\, volt$ source. The power consumed by the $6\,\Omega $ resistor is ........... $W$

If three bulbs $60\,W$, $100\,W$ and $200\,W$ are connected in parallel, then

The resistance of hot tungsten filament is about $10$ times the cold resistance. What will be the resistance of $100\, W$ and $200\, V$ lamp when not in use ............. $\Omega $

A $5\;ampere$ fuse wire can withstand a maximum power of $1\; watt$ in the circuit. The resistance of the fuse wire is