When the power delivered by a $100\,V$ battery is $40\,W$,the equivalent resistance of the circuit is ........... $\Omega$.

Power $P$ is to be delivered to a device via transmission cables having resistance $R_C$. If $V$ is the voltage across the device and $I$ is the current through it,find the power wasted and how can it be reduced.

The maximum power drawn from a source with electromotive force $E$ and internal resistance $r$ is given by:

Two electric bulbs rated $P_1 \text{ watt}, V \text{ volts}$ and $P_2 \text{ watt}, V \text{ volts}$ are connected in parallel and $V \text{ volts}$ are applied to the combination. The total power consumed will be:

$A$ heater of $220\, V$ heats a volume of water in $5\, \text{min}$ time. $A$ heater of $110\, V$ heats the same volume of water in ............... $\text{min}$.

$A$ current of $2\, A$ passing through a conductor produces $80\, J$ of heat in $10$ seconds. The resistance of the conductor is ............ $\Omega$.