2021SPp2q8 - Which appliance uses most energy (using P = V^2/R to explain)

Resistors may be connected in series or parallel. When asked which resistor has higher power (hence higher energy), in general we will think of using P = IV. But when using P = IV, it cannot relate to resistance R of the resistors directly.

Hence it will be more appropriate for us to P = I^2R or P = V^2/R.

For resistors in series, the current is the same. Hence it will be more direct to compare P and R using P = I^2R, where P is directly proportional to R.

For resistors in parallel, the p.d. is the same. Hence it will be more direct to compare P and R using P = V^2/R, where P is inversely proportional to R.