Which of the following is not a correct Ohm's Law formula?

• A. E = P x I
• B. V = I x R
• C. R = V / I
• D. V = P / I

Answer: (A)

The main idea tested is the set of relationships that connect voltage, current, and resistance in Ohm’s law, plus how power relates to those quantities. Ohm’s law gives V = I R and, rearranged, R = V / I. Power relates to voltage and current as P = V I.

The expression E = P x I is not a valid Ohm’s law form because it mixes power with current to imply a voltage, which doesn’t fit the V = I R relationship. If you substitute P = V I into that expression, you’d get E = V I^2, which does not equal V in general. In contrast, the other forms—V = I R and R = V / I—are direct expressions of Ohm’s law, and V = P / I is a correct rearrangement of the power relation P = V I. That’s why the first option is not a correct Ohm’s law formula.