What is the formula for voltage in relation to current and resistance?

• A. V = I/R
• B. V = IR
• C. I = VR
• D. R = VI

Answer: (B)

Voltage is determined by Ohm’s law: the voltage across a conductor equals the current through it times its resistance. So the correct relation is V = IR. This means the voltage you need to push a certain current through a given resistance is the product of that current and the resistance. For example, with 2 amperes flowing through 6 ohms, the voltage across the component is 12 volts (2 × 6 = 12).

The other forms don’t fit because they mix up the relationship or use the wrong units. V = I/R would divide current by resistance and wouldn’t give volts. I = VR would multiply voltage by resistance to equal current, which doesn’t match units or the actual relationship. R = VI would multiply voltage by current to give resistance, also incorrect.