An electric kettle has two coils. When one of these is switched on, the water in the kettle boils in $6\,\min$ . When the other coil is switched on, the water boils in $3\,\min$. If the two coils are connected in series, the time taken to boil the water in the kettle is ............. $min$
$3$
$6$
$2$
$9$
Two electric bulbs marked $40\,W,$ $220\,V$ and $60\,W,\,\,220\,V$ when connected in series across same voltage supply of $220\,V,$ the effective power is $P_1$ and when connected in parallel, the effective power is $P_2.$ Then $\frac {P_1}{P_2}$ is
If in the circuit, power dissipation is $150\, W$, then $R$ is ............... $\Omega$
If $2.2\,kW$ power is transmitted through a $100\,\Omega $ line at $22,000\,V,$ the power loss in the form of heat will be ............. $W$
Figure shows three resistor configurations $R_1,R_2$ and $R_3$ connected to $3\,V$ battery. If the power dissipated by the configuration $R_1, R_2$ and $R_3$ is $P_1, P_2$ and $P_3$ , respectively then
There are two electric bulbs of $40\, W$ and $100\, W$. Which one will be brighter when first connected in series and then in parallel,