When given voltage and resistance, how do you calculate current?

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

Answer: (A)

Ohm’s Law ties together voltage, current, and resistance: the current flowing through a conductor is equal to the voltage across it divided by its resistance. This means I = V / R, with current in amperes, voltage in volts, and resistance in ohms. The driving force (voltage) pushes charges, while resistance slows them down; increasing voltage raises current, and increasing resistance lowers current.

For a quick check, if you have 12 volts across a 6-ohm resistor, the current is 12 ÷ 6 = 2 amperes.

The other expressions don’t represent current correctly: dividing resistance by voltage yields a quantity with incorrect units for current, multiplying voltage by resistance gives a product with no direct meaning for current, and subtracting resistance from voltage isn’t a valid relationship for current.