Ohm’s law states that V = IR, where V is the voltage measured across a conductor, I is the current through the conductor, and R is the conductor’s resistance. In the image mnemonic at left (easily remembered by the word “viral”), covering any of the unknowns gives the formula in terms of the remaining parameters: V = IR, I = V/R, R = V/I.

Wikimedia user CMG Lee has devised other mnemonics in the same style for high-school physics students (right). For example, F = ma, m = F/a, a = F/m. In the corresponding SVG file you can hover over a symbol to see its meaning and formula.