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Plane polarisation
● VERBATIM — examined word-for-wordA wave is plane polarised when its oscillations are confined to one direction only, in a plane normal to the direction of energy transfer. A phenomenon of transverse waves only.
What this actually means
An unpolarised transverse wave wobbles in every direction perpendicular to travel. Polarising it means confining that wobble to one single direction, for example vertical only.
The oscillation direction always lies in the plane at right angles to the energy direction. That clause is part of the definition and worth a mark.
Only transverse waves qualify, because only they have oscillations in that perpendicular plane to restrict in the first place.
Prove it — watch it be true
- Start with the transverse wave oscillating in one plane
- Rotate the polariser: transmission is full when aligned, zero when crossed
- One surviving oscillation direction, perpendicular to travel — that is plane polarisation