Ohm's law and power practice
Given two of the quantities, find the third. Type your answer and it is marked on the spot, with the working shown if you miss. A sensible rounding still counts.
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The two laws it drills
Ohm's law: V = I × R. Rearranged, I = V ÷ R and R = V ÷ I. The power law: P = V × I. That is everything you need for these questions. Worked example: a load on 120 V drawing 2.5 A has a resistance of 120 ÷ 2.5 = 48 Ω and dissipates 120 × 2.5 = 300 W. Every rearrangement in the so-called power wheel is just algebra on these two statements.
Questions people ask
What is Ohm's law?
Voltage equals current times resistance: V = I × R. Rearranged, I = V ÷ R and R = V ÷ I. It ties the three basic quantities of a circuit together, so knowing any two gives you the third.
Where does power come in?
Power is voltage times current: P = V × I. Combine it with Ohm's law and you also get P = I² × R and P = V² ÷ R. This drill sticks to the two core forms so the relationships stay clear.
Do I need to memorise the wheel?
Not really — if you hold V = I × R and P = V × I, everything else is algebra on those two. The "wheel" is just every rearrangement drawn in a circle. Drill the two core laws and the rest falls out.
Related
- Series vs parallel lighting — where the voltage sharing shows up.
- Formula sheets — the Ohm's law and power wheel, printable.
- All drills
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