---
title: "Polarisation as Evidence for Transverse Waves"
description: "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."
canonical: https://lightmysky.com/learn/science/polarisation-as-evidence-for-transverse-waves-mt_mCbxv77qDA
source: https://lightmysky.com/learn/science/polarisation-as-evidence-for-transverse-waves-mt_mCbxv77qDA.md
retrieved: 2026-09-12
---

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# 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.

Subject: Science · Area: Waves, Light & Sound · Ages 16 to 17
Page: https://lightmysky.com/learn/science/polarisation-as-evidence-for-transverse-waves-mt_mCbxv77qDA

## Ready when they can

- 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

## Lesson: Polarised light proves waves go sideways

Polarisation means a wave's oscillations keep one definite direction. Only transverse waves can be polarised, so the test separates transverse from longitudinal.

**Example.** 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.

**Tip.** 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.

**Recap.** Filters pass one direction only, which is why polarisation proves light is transverse.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Progressive Waves: Phase and Path Difference](https://lightmysky.com/learn/science/progressive-waves-phase-and-path-difference-mt_RotpycCNF8)

## Opens up

- [Chirality, R and S Assignment and Optical Activity](https://lightmysky.com/learn/science/chirality-r-and-s-assignment-and-optical-activity-mt_-p-7uFBTDt)
- [Superposition and Stationary Waves](https://lightmysky.com/learn/science/superposition-and-stationary-waves-mt_AIxA2TYGJN)