The basics of Ohm's Law are easy if you remember the Eagle, the Indian, and the Rabbit.
The Eagle -- "E" -- is electromotive force, measured in Volts.
The Indian -- "I" -- is current flow, measured in Amps.
The Rabbit -- "R" -- is resistance, measured in Ohms.
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Eagle
Indian Rabbit
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The Eagle looks down and sees the Indian and the Rabbit side-by-side. ==> E=I*R
The Indian looks up and sees the Eagle over the Rabbit. ==> I=E/R
The Rabbit looks up and sees the Eagle over the Indian. ==> R=E/I
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If you know two of the variables, you can easily solve for the third.
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Bonus pic for visual learners:
Scott