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 $20\ min$?

$A$ $12 \text{ HP}$ motor has to be operated $8 \text{ hours/day}$. How much will it cost at the rate of $50 \text{ paisa/kWh}$ in $10$ days? (in $Rs.$)

$A$ resistance $R = 12 \, \Omega$ is connected across a source of $emf$ as shown in the figure. Its $emf$ changes with time as shown in the graph. What is the heat developed in the resistance in the first four seconds (in $, J$)?

If voltage across a bulb rated $220 \,V, 100 \,W$ drops by $2.5 \%$ of its rated value, then the percentage of the rated value by which the power would decrease is (in $\%$)

In India,electricity is supplied for domestic use at $220\,V$. It is supplied at $110\,V$ in the $USA$. If the resistance of a $60\,W$ bulb for use in India is $R$,then the resistance of a $60\,W$ bulb for use in the $USA$ will be:

$A$ 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