Ohmic material

The CED is careful with the word. Ohm's law relates current, resistance and potential difference across a conductive element, $I = \Delta V / R$, and then 11.3.B.1.i adds the qualifier: materials that obey Ohm's law have constant resistance for all currents and are called ohmic materials. Identical wording sits in AP Physics 2 and in AP Physics C: Electricity and Magnetism.

The test is a graph, and the CED names it. Statement 11.3.B.1.iv says the resistance of an ohmic element can be determined from the slope of a graph of the current in the element as a function of the potential difference across it. Read that axis order carefully: with $I$ up the vertical axis and $\Delta V$ along the horizontal, the slope is $1/R$, so a steeper line means a smaller resistance. Any curve at all means the element is not ohmic.

Temperature is where the CED sets two of its own statements against each other, deliberately. The resistivity of a conductor typically increases with temperature (11.3.A.2.ii), but the resistivity of an ohmic material is constant regardless of temperature (11.3.B.1.ii). One describes real copper; the other describes the model. A hot filament genuinely bends its line.

Which you get is decided by the equation sheet, not by the physics: both the AP Physics 2 and the AP Physics C: E&M sheets list among their exam conventions that resistors and lightbulbs are ohmic. So assume linearity unless a question hands you data that is not.

Rearranging and solving belongs to the Ohm's law guide and the calculator.