Joule Heating And Energy

Joule's law of heating states that the heat produced in a resistor equals $H=I^{2}Rt$, where the power dissipated is $I^{2}R$ and $t$ is the time, a result established in NCERT Class 12, Chapter 3 (Current Electricity). First convert the time to seconds: $t=5\text{ minutes}=300$ s. The power dissipated is $I^{2}R=2^2\times 20=4\times 20=80$ W. Multiplying by time gives $H=80\times 300=24000$ J. The option 400 J results from carelessly using $t=5$ s instead of converting the five minutes into 300 seconds. The option 8000 J mistakenly uses $I\times R\times t$ without squaring the current, dropping a crucial factor of the current. The option 1200 J comes from omitting the resistance term altogether and computing only a partial product of current and time. A plausibility check confirms the magnitude: a resistor steadily dissipating 80 W for five full minutes should release on the order of tens of kilojoules, and 24000 J sits comfortably in that range, while the dimensions of joules equalling watts times seconds are entirely sound, so the result is trustworthy in both size and units.