$A$ railway compartment is lit up by thirteen lamps,each taking $2.1\,A$ at $15\,V$. The heat generated per second in each lamp will be ............ $cal$.

The battery of a mobile phone is rated as $4.2 \ V, 5800 \ mAh$. How much energy is stored in it when fully charged (in $kJ$)?

What amount of heat will be generated in a coil of resistance $R$ due to a charge $q$ passing through it if the current in the coil decreases to zero uniformly during a time interval $\Delta t$?

Water boils in an electric kettle in $20$ minutes after being switched on. Using the same main supply,the length of the heating element should be . . . . . . to . . . . . . times of its initial length if the water is to be boiled in $15$ minutes.

The maximum current that flows through a fuse wire before it blows out varies with its radius as

From where does electrical power derive? Explain it.