How many calories of heat will be produced approximately in a $210\, W$ electric bulb in $5$ minutes?

Water in an electric kettle starts boiling in $15 \ min$ after being switched on. If the length of the heating wire is reduced to $2/3$ of its original length,the time taken to boil the same amount of water will be ........... $min$.

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 ............. $watt$.

$Kilowatt-hour$ $(kWh)$ is a unit of

Two electric lamps of $40\, W$ each are connected in parallel. The power consumed by the combination will be ........... $W$.

$A$ $12 \text{ HP}$ motor has to be operated $8 \text{ hours/day}$. How much will it cost at the rate of $50 \text{ paisa/kWh}$ in $10$ days? (in $Rs.$)