Which equation expresses Ohm's law for a resistor?

Which equation expresses Ohm's law for a resistor?

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

Answer: (A)

Voltage across a resistor is proportional to the current through it, with the resistance acting as the proportionality constant. That gives the standard form of Ohm’s law for a resistor: V = IR. This means the voltage you measure across the resistor equals the current through it times its resistance. The relationship is linear, so doubling the current doubles the voltage if the resistance stays the same, and the units work out correctly (ohms times amps give volts). The other forms don’t match how voltage, current, and resistance relate: they either mix up the variables or produce incorrect units. For example, I = VR would imply current equals voltage times resistance, which isn’t dimensionally consistent; V = R/I and V = I/R misplace the variables, violating the established V = IR relationship. If you know I and R, you can find V via V = IR; if you know V and R, you can find I via I = V/R.

Voltage across a resistor is proportional to the current through it, with the resistance acting as the proportionality constant. That gives the standard form of Ohm’s law for a resistor: V = IR. This means the voltage you measure across the resistor equals the current through it times its resistance. The relationship is linear, so doubling the current doubles the voltage if the resistance stays the same, and the units work out correctly (ohms times amps give volts).

The other forms don’t match how voltage, current, and resistance relate: they either mix up the variables or produce incorrect units. For example, I = VR would imply current equals voltage times resistance, which isn’t dimensionally consistent; V = R/I and V = I/R misplace the variables, violating the established V = IR relationship. If you know I and R, you can find V via V = IR; if you know V and R, you can find I via I = V/R.