Which device can convert all electrical energy into heat?

An electric kettle takes $4 \ A$ current at $220 \ V$. If the entire electric energy is converted into heat energy, then the time (in minutes) taken to increase the temperature of $1 \ kg$ of water from $34^{\circ} C$ to $100^{\circ} C$ is

An electric bulb is marked $100\ W, 230\ V$. If the supply voltage drops to $115\ V$,how much heat (in $J$) is produced by the bulb in $20\ min$?

$A$ $100\, W$ bulb working on $200\, V$ and a $200\, W$ bulb working on $100\, V$ have:

$A$ $220\, V$,$1000\, W$ bulb is connected across a $110\, V$ mains supply. The power consumed will be ............ $W$.

The emf of a battery is $2\, V$ and its internal resistance is $0.5 \,\Omega$. The maximum power which it can deliver to any external circuit will be ............. $watt$.