Which of the following is not a valid expression of Ohm's law?

Ohm's law defines the relationship between voltage (E or V), current (I), and resistance (R) in an electrical circuit. The law is typically expressed with the formula V = IR, which articulates that voltage equals current multiplied by resistance. Each of the other options correctly represents relationships defined by Ohm's law.

In the first choice, while R is expressed as either R = EI or R = VI, this does not align with the standard formulations of Ohm's law. The E in this expression is intended to denote either electromotive force or voltage, which can cause confusion as the standard is to utilize V. Hence, these expressions are not accurate representations of Ohm's law.

Subsequent options accurately derive resistance from the established relationships: the second expresses voltage as a function of current and resistance, the third reorganizes the formula to find current in terms of voltage and resistance, and the fourth correctly presents resistance calculated as voltage over current. Each of these formulations maintains consistency with Ohm's law, further affirming that the first option fails to do so.