Which formula correctly expresses voltage drop in a circuit?

Which formula correctly expresses voltage drop in a circuit?

• A. V_drop = R × I
• B. V_drop = P × I
• C. V_drop = I × R
• D. V_drop = I + R

Answer: (C)

Voltage drop across a resistor follows Ohm's law: the drop equals the current through the element times its resistance. In symbols, V_drop = I × R. This matches the units volts = amps × ohms. The order doesn’t change the value (R × I would give the same result), but the conventional way to express it is V = IR, with the current first. The other expressions don’t represent voltage drop: multiplying by power (P × I) isn’t a voltage, and adding I and R combines unlike quantities.

Voltage drop across a resistor follows Ohm's law: the drop equals the current through the element times its resistance. In symbols, V_drop = I × R. This matches the units volts = amps × ohms. The order doesn’t change the value (R × I would give the same result), but the conventional way to express it is V = IR, with the current first. The other expressions don’t represent voltage drop: multiplying by power (P × I) isn’t a voltage, and adding I and R combines unlike quantities.