$A$ lamp is rated at $240 \ V, 60 \ W$. When in use,the resistance of the filament of the lamp is $20$ times that of the cold filament. The resistance of the lamp when not in use is: (in $\Omega$)

$A$ battery with $EMF$ $E$ and internal resistance $r$ is connected across a resistance $R$. The power consumption in $R$ will be maximum when:

$A$ 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.

$A$ constant voltage is applied between the two ends of a metallic wire. If both the length and the radius of the wire are doubled, the rate of heat developed in the wire

Two electric bulbs have tungsten filaments of the same length. If one of them is rated $60\ W$ and the other $100\ W$,then:

What is the value of $1 \, kWh$ in Joules?