Ohm's Law & Power

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Any two of voltage, current, resistance and power give the other two, with the units used per hour

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Which two do you know

What you have

Voltage (V)

Current (A)

All four

Voltage

12.0000 V

Current

2.0000 A

Resistance

6.0000 Ω

Power

24.0000 W

The formulas

Ohm's law: V = I × R
Power: P = V × I
Power from resistance: P = I²R = V²⁄R
Units used in an hour: 0.0240 kWh

Any two of the four give you the other two. The last line is the one that matters on an electricity bill: watts divided by a thousand gives kilowatts, and multiplied by hours gives the units you are charged for.

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