2.3.46 - Critical angle

Calculate critical angle using sin C = 1/n.

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

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

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

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