An electric bulb is rated $220\, volt$ and $100\, watt$. Power consumed by it when operated on $110\, volt$ is ............. $watt$

Heater of electric kettle is made of a wire of length $L$ and diameter $d$. It takes $4$ minutes to raise the temperature of $0.5 \ kg$ water by $40\ K$. This heater is replaced by a new heater having two wires of the same material, each of length $L$ and diameter $2 d$. The way these wires are connected is given in the options. How much time in minutes will it take to raise the temperature of the same amount of water by $40K$ ?

$(A)$ $4$ if wires are in parallel

$(B)$ $2$ if wires are in series

$(C)$ $1$ if wires are in series

$(D)$ $0.5$ if wires are in parallel.

Two bulbs of equal wattage, one having carbon filament and the other having a tungsten filament are connected in series to the mains, then

A hot electric iron has a resistance of $80\,\Omega $ and is used on a $200\, V$ source. The electrical energy spent, if it is used for two hours, will be  ........... $Wh$

If the length of the filament of a heater is reduced by $10\%$, the power of the heater will

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