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.

Two resistors of $6\,\Omega $ and $9\,\Omega $ are connected in series to a $120\, volt$ source. The power consumed by the $6\,\Omega $ resistor is ........... $W$

An electric kettle takes $4\, A$ current at $220\, V$. How much time will it take to boil $1\, kg$ of water from room temperature $20\,^\circ C$ ? The temperature of boiling water is $100\,^\circ C$ .................. $minutes$

A $50 \,W$ bulb connected in series with a heater coil is put to an $AC$ mains. Now the bulb is replaced by a $100 \,W$ bulb. The heater output will ...........

What will happen when a $40\, watt$, $220\, volt$ lamp and $100\, watt$, $220\, volt$ lamp are connected in series across $40\, volt$ supply

The same mass of copper is drawn into two wires $1\, mm$ and $2\, mm$ thick. Two wires are connected in series and current is passed through them. Heat produced in the wire is in the ratio