An electric heater heats a certain amount of water in $5 \, \text{min}$ when connected to a $220 \, \text{V}$ supply. How many minutes will it take to heat the same amount of water when connected to a $110 \, \text{V}$ supply?

Four wires of the same diameter are connected in turn between two points,maintained at a constant potential difference. Their resistivities and lengths are: $\rho$ and $L$ (wire $1$),$1.2\rho$ and $1.2L$ (wire $2$),$0.9\rho$ and $0.9L$ (wire $3$),and $\rho$ and $1.5L$ (wire $4$). Rank the wires according to the rates at which energy is dissipated as heat,greatest first.

$A$ current of $2\, mA$ was passed through an unknown resistor which dissipated a power of $4.4\, W$. The dissipated power when an ideal power supply of $11\, V$ is connected across it is:

Which device can convert all electrical energy into heat?

An electric bulb is rated $60\,W$,$220\,V$. The resistance of its filament is ............. $\Omega$.

The energy consumed in a $1\, kW$ electric heater in $30$ seconds will be: