Two bulbs have resistances in the ratio $1 : 2$. They are connected in parallel to a constant voltage source. What is the ratio of power dissipated in them?

Two electric bulbs are connected one by one across a potential difference $V$. At that time,the power consumed in them is $P_1$ and $P_2$ respectively. Now,if the potential difference $V$ is applied across the series combination of these bulbs,what will be the total power consumed?

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.

An amount of charge $Q$ passes through a coil of resistance $R$. If the current in the coil decreases to zero at a uniform rate during time $T$,then the amount of heat generated in the coil will be,

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.