An electrical cable having a resistance of $0.2 \Omega$ delivers $10 \text{ kW}$ at $200 \text{ V}$ $D$.$C$. to a factory. What is the efficiency of transmission (in $\%$)?

$A$ constant potential difference is applied to the ends of a graphite rod, whose resistance decreases with a rise in temperature. The rod can be $(1)$ covered with asbestos or $(2)$ left open to the atmosphere. Answer for the steady state.

Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with the increase in temperature. If at room temperature,$100 \ W$,$60 \ W$ and $40 \ W$ bulbs have filament resistances $R_{100}$,$R_{60}$ and $R_{40}$,respectively,the relation between these resistances is

$A$ 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 ........... $min$.

The ratio of cross-sectional areas of two conducting wires made up of the same material and having the same length is $1 : 2$. What will be the ratio of heat produced per second in the wires,when the same current is flowing in them?