Which statement describes Ohm's law for a linear resistor?

• A. Voltage is proportional to current with constant resistance.
• B. Current is independent of voltage.
• C. V/I varies with current.
• D. Power equals voltage times resistance.

Answer: (A)

For a linear resistor, Ohm's law states that the voltage across the resistor equals the current through it times a constant resistance: V = I R. This means the voltage is directly proportional to the current, and the proportionality constant R does not change over the operating range. In other words, the ratio V/I stays the same, equal to R, no matter what the current is (as long as the resistor remains in its linear region).

That is exactly what the statement describes: voltage is proportional to current with constant resistance. The other statements don’t fit because a linear resistor does not have current independent of voltage, the ratio V/I does not vary with current, and power is not defined as voltage times resistance (the correct power relation is P = VI, or equivalently P = I^2R or P = V^2/R).