How many joules are there in one kilowatt-hour?

The $V-I$ graphs for two wires $A$ and $B$ are shown in the figure. If we connect both the wires one by one to the same battery, which of the two will produce more heat per unit time? Give justification for your answer.

Several electric bulbs designed to be used on a $220\, V$ electric supply line,are rated $10\, W$. How many lamps can be connected in parallel with each other across the two wires of a $220\, V$ line if the maximum allowable current is $5\, A$?

Find the minimum rating of fuse that can be safely used on a line on which two $1.1 \, kW$ electric geysers are to run simultaneously. The supply voltage is $220 \, V$. (in $A$)

$A$ fuse is a $.......$ wire.

Define electric power. Give its $SI$ units and write its mathematical equation.