Which formula gives resistance in terms of voltage and current?

• A. R = I / V
• B. R = V / I
• C. R = V * I
• D. R = I * V

Answer: (B)

Ohm’s law relates voltage, current, and resistance, with V = I R. To solve for resistance, divide both sides by I, giving R = V / I. This arrangement makes sense because resistance is the ratio of voltage to current, and the units volts per ampere are defined as the ohm. If voltage goes up while current stays the same, resistance must increase; if current increases with the same voltage, resistance must decrease. The other forms don’t describe resistance: I divided by V gives conductance, V times I gives power, and I times V is also power. So R = V / I is the correct expression.