An electric bulb works on the heating effect of current.

Which uses more energy, a $250 \,W$ $TV$ set in $1 \,hr$ or a $1200 \,W$ toaster in $10$ minutes?

$1 \; kWh = \ldots \ldots \ldots \; \text{watt-seconds}$

Define one watt.

Two bulbs are marked $60\, W, 220\, V$ and $100\, W, 220\, V$. These are connected in parallel to a $220\, V$ mains. Which one out of the two will glow brighter?

The applied potential difference across a given resistor is altered so that the heat produced per second increases by a factor of $16.$ By what factor does the applied potential difference change?