$A$ $500\, W$ heating unit is designed to operate from a $115\, V$ line. If the line voltage drops to $110\, V$,the percentage drop in heat output will be ............... $\%$

When the power delivered by a $100\,V$ battery is $40\,W$,the equivalent resistance of the circuit is ........... $\Omega$.

An electric bulb is marked $100\ W, 230\ V$. If the supply voltage drops to $115\ V$,how much heat (in $J$) is produced by the bulb in $20\ min$?

The figure shows a thick spherical shell made of a material with electrical conductivity $\sigma$. It has inner and outer radii of $10\ cm$ and $20\ cm$ respectively and is filled with ice inside. Its inner and outer surfaces are kept at different potentials by a battery with internal resistance $r = \frac{2}{\pi}\ \Omega$ and electromotive force $\epsilon = 5\ V$. Find the value of $\sigma$ for which the ice melts at the maximum possible rate,given that $25\%$ of the heat generated by the shell due to Joule heating is used to melt the ice.

The heat produced per unit time,on passing electric current through a conductor at a given temperature,is directly proportional to . . . . . . .

The voltage of clouds is $4 \times 10^6 \, V$ with respect to the ground. In a lightning strike lasting $100 \, ms$,a charge of $4 \, C$ is delivered to the ground. The power of the lightning strike is