24.1.1—A piezo-electric crystal changes shape when a p.d. is applied across it and

understand that a piezo-electric crystal changes shape when a p.d. is applied across it and that the crystal generates an e.m.f. when its shape changes.

Use —a piezo-electric crystal changes shape when a p.d. is applied across it and to connect the rule to the data and decision in the question.

This matters because —a piezo-electric crystal changes shape when a p.d. is applied across it and determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —a piezo-electric crystal changes shape when a p.d. is applied across it and to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —A piezo-electric crystal changes shape when a p.d. is applied across it and is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.