Polarisation as Evidence for Transverse Waves
Only a transverse wave can be restricted to one plane of oscillation, so light that a second filter can block must be transverse. The same test performed on sound gives nothing.
What a learner can do afterwards
- Predicts the brightness through two filters as one is turned, including the fully blocked position
- Names polarisation behind glare reduction in sunglasses and behind aerial alignment
- Explains why sound cannot be polarised and what that shows about it
1 · Read
Polarisation means a wave's oscillations keep one definite direction. Only transverse waves can be polarised, so the test separates transverse from longitudinal.
Send light through two filters. Aligned, they pass it; turn one to ninety degrees and they block it fully. Try the same test on sound and nothing changes, since sound is longitudinal.
Sunlight mixes all directions, while a filter passes one direction like slits passing one rope wave. Reflected glare is partly polarised, so sunglasses block that direction and cut the dazzle.
Aerials turn to face the signal because only the matching alignment gets through strongly. If rotating a filter changes nothing, the wave is not transverse.
Filters pass one direction only, which is why polarisation proves light is transverse.
2 · Watch
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Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.