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Ohm's law for alternating current

Ohm's Law is a very simple and useful tool for analyzing electric circuits. It is used so often in the study of electricity and electronics that it needs to be committed to memory by the serious student. For those who are not yet comfortable with algebra, there's a trick to remembering how to solve for any one quantity, given the other two. First, arrange the letters E, I, and R in a triangle like this:

If you know E and I, and wish to determine R, just eliminate R from the picture and see what's left:

If you know E and R, and wish to determine I, eliminate I and see what's left:

Lastly, if you know I and R, and wish to determine E, eliminate E and see what's left:

Eventually, you'll have to be familiar with algebra to seriously study electricity and electronics, but this tip can make your first calculations a little easier to remember. If you are comfortable with algebra, all you need to do is commit V=IR to memory and derive the other two formulae from that when you need them!

  • Voltage measured in volts, symbolized by the letters "E" or "V".
  • Current measured in amps, symbolized by the letter "I".
  • Resistance measured in ohms, symbolized by the letter "R".
  • Ohm's Law: V = IR ; I = V/R ; R = V/I