In the circuit shown, the resistance $r$ is a variable resistance. If for $r = fR,$ the heat generation in $r$ is maximum then the value of $f$ is
$\frac {1}{4}$
$1$
$\frac {1}{2}$
$\frac {3}{4}$
A rise of temperature of $4\,^oC$ is observed in a conductor by passing a current. If the current is tripled, the rise temperature will be .............. $^oC$
Two heaters $A$ and $B$ have power rating of $1 \mathrm{~kW}$ and $2 \mathrm{~kW}$, respectively. Those two are first connected in series and then in parallel to a fixed power source. The ratio of power outputs for these two cases is:
Two identical bulbs are connected in parallel across an ideal source of emf $E$. The ammeter $A$ and voltmeter $V$ are ideal. If bulb $B_2$ gets fused, then
Watt-hour meter measures
Two electric bulbs have tungsten filament of same length. If one of them gives $60\ W$ and the other $100\ W$ , then