2.4.71 - Resistivity

Use R = ρl/A for the resistance of a uniform conductor.

Use - resistivity to connect the rule to the data and decision in the question.

This matters because - resistivity determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - resistivity to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Resistivity is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.