What is the formula for Ohm's Law?

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

Answer: (A)

Voltage equals current through the conductor multiplied by its resistance. This simple relationship shows how the driving force (voltage) pushes charge through a material that offers opposition (resistance). If you know the current and resistance, you can find the voltage; if you know voltage and resistance, you can find the current. For example, a 5-ohm resistor with 3 amperes of current will have a voltage drop of 15 volts across it.

The same relationship can be rearranged: current equals voltage divided by resistance, and resistance equals voltage divided by current. A related idea is that electrical power is voltage times current, and you can derive P = I^2R or P = V^2/R from V = IR. Remember that this applies to linear, resistive components; non-linear devices may not follow the simple V = IR form.