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Test for plane polarisation
● VERBATIM — examined word-for-wordRotate a polaroid between beam and detector through at least 180°: intensity falling to zero at some orientation ⇒ plane polarised; constant intensity ⇒ unpolarised. Stock 2-marker, exact phrasing.
What this actually means
The stock two-marker: place a polaroid between the beam and a detector and rotate it through at least 180°. Intensity falling to zero at some orientation means plane polarised; intensity never varying means unpolarised.
180° is enough because cos² repeats every 180°; a full turn shows nothing new.
Give the observation AND the conclusion together; the mark scheme pairs them.
Prove it — watch it be true
- Send polarised light in and rotate the analyser through 180°
- The meter dips to exactly zero once: verdict, plane polarised
- Swap to unpolarised light: the meter never moves — that constancy is the other verdict