$A$ room heater is rated $400 \text{ W}$, $220 \text{ V}$. If the supply voltage drops to $200 \text{ V}$, what will be the power consumed (approximately) (in $\text{ W}$)?

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 ........... $min$.

An electric lamp is marked $60\, W$, $230\, V$. The cost of $1\, kWh$ of power is Rs. $1.25$. The cost of using this lamp for $8$ hours is Rs. ................

$n$ identical bulbs,each designed to draw a power $P$ from a certain voltage supply,are joined in series across that supply. The total power which they will draw is

Heating coils rated at $220\, V$ are available with resistances of $55\,\Omega$,$110\,\Omega$,$220\,\Omega$,and $440\,\Omega$. Which resistance value will produce the maximum power?

$A$ total charge $Q$ flows across a resistor $R$ during a time interval $T$ in such a way that the current vs. time graph for $0 \rightarrow T$ is like the loop of a sine curve in the range $0 \rightarrow \pi$. The total heat generated in the resistor is