Which formula gives voltage across a resistor?

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

Answer: (B)

Ohm's law links voltage, current, and resistance. For a resistor, the voltage drop across it is the current through it times its resistance: V = I × R. This directly shows how much voltage is present when you know the current and the resistance. The units line up as volts = amps × ohms, and the idea is intuitive: doubling the current (with the same resistance) doubles the voltage, or increasing the resistance (with the same current) increases the voltage as well. The other common forms, like R = V / I, I = V / R, or P = V × I, relate to resistance, current, or power, but the direct expression for voltage across a resistor is V = I × R.